CHAPTER 5

"Run simulation 'Summary,'" O'Brien ordered the holosuite.

"Program complete," responded the holosuite's voice. "Enter when ready."

The door of the suite opened. Dax and O'Brien waited for Sisko to enter, but first Sisko had to know something.

"You're sure Quark can't eavesdrop?"

"Quite sure." O'Brien smirked. "I've even set things up so that if he even explores the possibility of eavesdropping, we'd know about it."

Dax was skeptical. "I don't know, Quark can be pretty clever."

"And I'm not?" O'Brien smiled.

Sisko was reassured. He stepped into the holosuite. Dax and O'Brien followed, and the holosuite door closed behind them, then vanished.

They were standing in a starship corridor, facing a formidable door.

"This is the door to the Probe Preparation Bay," O'Brien announced. "Above the door is a medical scanner that checks you to be sure you are who you purport to be. It checks your DNA, your brain wave patterns, your fingerprints, and probably a few other things as well. If you aren't an authorized person, a member of the probe team, you can't get in."

"So how do we get in?" Dax wondered.

"In this simulation, we're all authorized persons. We go in one at a time. Remember, there will be three of us in there, though there are usually only supposed to be two, so things might be a little cramped." O'Brien stepped up to the door. "Miles O'Brien," he announced, and the door opened for him. O'Brien stepped through and the door closed.

Sisko announced his name and he too was admitted. Sisko saw that the entrance was actually a combination outer door and inner door. Once he stepped through the outer door, it closed, and an inner door promptly opened to admit him to the brightly lit Bay. Moments later, Sisko, Dax and O'Brien were standing in the Bay.

Sisko saw that the Bay was indeed cramped. There was room to move around, but not much. The only places to sit were jump seats mounted in the bulkheads. Various pieces of equipment and instruments lined the walls, some apparently permanently mounted in place. There were displays and tools in various locations. Sisko saw against one wall a boxy console that appeared to be a standard cargo scanner. The biggest obstacle in the Bay was a sturdy table in the center.

Sisko saw a structure on one wall that resembled a meter-long slot. A similar slot-like structure was present on another wall, and yet another similar structure was present on a third wall. Sisko wondered about the purpose of these slots.

"All right, this is the Probe Prep Bay," O'Brien began. "Here in the center is what they call 'the bench'; it is where the probe is prepared for launch."

"So all we need is a probe," Dax said.

"First, we need to receive authorization from the captain to access the Locker," O'Brien answered. "The Locker is just as secure as this Bay, in some ways, even more secure. Probes are loaded into and unloaded from the Locker by automation. No personnel are allowed inside the Locker, ever. Any attempt by anyone to break into the Locker will result in all probe seals breaking, and then the probes become utterly useless."

"What does 'seals breaking' mean?" Dax asked. "I didn't see anything about that in the materials that I read."

"There's a little bit about it in our library computer," O'Brien said. "Basically, a probe can self-destruct under certain conditions. It self-destructs non-explosively. Self-destruct can be triggered automatically or by express command. There are various sealed compounds inside each probe, and if those seals break, the compounds get released and much of the interior of the probe gets, well, scrambled."

"So that the probe is no longer functional?"

"That's right, but it goes beyond that. Not only will the probe never explode, the interior components get so fouled up that no one ought to be able to reverse-engineer how the probe was put together in the first place. It's possible that the explosion inside Observer's Probe Preparation Bay was interpreted as an attack or as an attempt to break into the Locker, and that is what caused all the probes automatically to break their seals. Anyway, as I said, the first thing we need is authorization from the captain, so let's get it. Preparation Bay to captain."

A synthetic voice answered immediately. "Captain here."

"Request authorization to access the Locker."

"Access granted, access grant logged."

"Thank you, Preparation Bay out." O'Brien turned to Sisko. "The probe team only needs to do that at the start of the mission. They don't need to do it with every probe they prepare. Okay, now that we're authorized by the captain, let's get a probe. Computer, dispense probe, authorization 'O'Brien one-two-three.'"

A different synthetic voice answered. "Authorization accepted. Stand by."

O'Brien gestured to the slot on the wall, which after about half a minute changed its shape and produced a substantially cylindrical object, resting on end in a small cradling platform. "That's the probe in the receptacle."

Sisko leaned over to examine the probe, but O'Brien spoke up. "Stay where you are, sir." As Sisko leaned back, a strange-looking robotic mechanism descended from the ceiling and attached itself to the probe. It only took about a second for this mechanism to lift the probe from the receptacle. "The probe is too heavy to lift, sir," O'Brien explained. "There's a crane in the ceiling that lifts each probe to the bench."

By the time O'Brien finished his sentence, the crane had done just that, and its lifting mechanism had been withdrawn. The probe stood on end on the bench.

The probe's exterior seemed to be mostly white metal, Sisko guessed. The probe's shape was essentially cylindrical with a tapered nose, and there were numerous protrusions and ridges and other structures all over it.

Sisko decided to touch the probe. It felt hard and smooth like metal, but in a way, it didn't feel like metal at all.

"In case you're wondering, sir," O'Brien said, "that casing makes it difficult to transport the probe with a transporter, and makes it harder to grab with a tractor beam. Makes it harder to steal. The casing also includes features that make the probe difficult to scan when the seals are intact, but our scanner knows where those features are and can scan around them."

Just one of the many security schemes, Sisko thought. "So, now that the probe is here, what do we do?"

O'Brien sighed. "So now we go through the preparation checklist. It's a rather tedious process, I'm afraid. First, we have to let the system do a preliminary automatic diagnostic and scan. I'm not sure what this scan checks for, but I'd wager that pretty much every system and subsystem gets checked multiple times. As you can see on this indicator, the first automatic scan is now complete, and diagnostic results are within normal limits. And so we can now remove the first mechanical."

"The first mechanical what?" Dax wanted to know.

"The first mechanical safety." O'Brien saw Sisko and Dax exchange glances, so he explained: "Believe it or not, this probe has several moving parts: hinges, levers, latches, push rods, that type of thing. That may sound like ancient technology, but these moving parts are very reliable, readily constrained, and very hard to manipulate remotely. The moving parts need to move in order for the probe to be able to detonate. This component here," O'Brien indicated a ring near the base of the probe, "holds some of those parts in fixed positions relative to one another, so that they cannot move, and since they cannot move, the probe cannot detonate."

O'Brien held up a fist. "Inside the probe is an element called a 'core.'" He held up his other fist. "There is also an element called a 'striker.' In order for the probe to detonate, the striker must physically strike the core." O'Brien demonstrated by hitting one fist with the other. "The composition of the core and the striker are perhaps the most closely guarded secrets in the entire galaxy, because it is their physical contact, impact, chemical reaction and surface interactions that ultimately cause the detonation resulting in Upsilon Radiation. The mechanical safeties prevent the striker from moving, relative to the core. Oh, and there is also a barrier physically interposed between the striker and the core, and until this barrier is moved out of the way, the striker cannot touch the core. But that gets moved later."

With that, O'Brien pulled the ring, twisted it, pushed it, twisted it again, then pulled. As O'Brien pulled the ring, a set of bonded metal rods was extracted from the probe.

"As I've said, this is very old-fashioned technology," O'Brien went on, "but it is also very secure. Mechanical safeties like this cannot be deactivated remotely, and," he banged the bonded rods on the bench, "they don't break. Now that the first mechanical is out, I need to use this, here." He picked a handheld crescent-shaped instrument from the wall. "Ready to scan," O'Brien announced, and then he moved the crescent slowly along the length of the probe.

"Repeat," said the computer, when O'Brien reached the end. O'Brien ran the instrument along the length of the probe again.

"Any idea what you're scanning for this time?" Dax asked.

"I'm not really scanning for anything. It's the scanner across from me that's doing the actual scanning, along with the auxiliary scanning elements in the bulkheads. The instrument I'm holding is simply a reflector. It is totally passive, it has no scanning emitter. If I had to guess, I'd say that this scan is checking the fuel in the propulsion systems."

Sisko noticed that O'Brien used the plural. "How many propulsion systems are there?"

"At least three. One to position the probe in the planet's atmosphere, and one to get the probe out of the planet's atmosphere if anything goes wrong. And the third system is a redundant backup." O'Brien glanced at one of the displays. "And it looks like whatever scans were done there, we passed." O'Brien returned the crescent-shaped instrument to its mount on the wall, and retrieved a hook-like piece of metal mounted next to it. "So we move on to the second mechanical."

O'Brien pressed on a protrusion and a small opening appeared next to it on the probe. O'Brien lowered the hook-like object into the opening, and turned it like a key. He then withdrew a long, gently curved metal rod from the probe. O'Brien performed this maneuver from a less-than-optimal angle; it might have been easier had the Bay not been so crowded.

"Here's the second mechanical, and you need a special tool like this to extract it. And now, yet another automatic scan and diagnostic are performed. These usually take several minutes to do."

"Chief," said Sisko, "when we've completed the checklist and done all the scans and removed all the safeties, will we be able to detonate the probe?"

"No."

"Because there are still some safety elements in place?"

"That's right, sir."

"Can we deactivate those other safety elements manually?"

O'Brien was about to say doing so would be impossible, but stopped himself. "I don't think so, sir. They're all protected from manipulation, and they're all tamper-proof. There's no way to get at them, no way to turn them off. And even if you could turn them off, it would do no good. Turning them off doesn't deactivate them, and the only thing that can deactivate them is the probe itself. The probe won't deactivate these safeties unless sensors in the probe affirmatively indicate an absence of life, and that the probe is deep in the atmosphere of a gas giant. Add to that, the probe has to receive an encrypted authorization to detonate, which comes from the Probe Control Station, not from this Bay."

"Where's the Probe Control Station?" Sisko asked.

"About ten decks up, I think. Probe Control is a secure area like the Bay, so only the probe team is allowed in. It's not shielded from sensors, though, like the Bay is. Anyway, the encrypted authorization deactivates some additional safety interlocks and allows the probe to execute a command to detonate. There must be an explicit command to detonate, and it too is issued by the Probe Control Station, not by anyone in the Bay."

"Scan suspended," announced the computer. "Attach phase buffer deactivator."

O'Brien retrieved a large cap-like object from the wall and placed it on the nose of the probe. The object was unwieldy and clearly did not fit, the way O'Brien had it. "Give me a hand with this, will you, sir? The deactivator needs to be positioned just so." With Sisko's help, the object was maneuvered into place on the probe.

"Deactivator placement is now correct," acknowledged the computer. "Scan commencing."

"But if all of the requirements of those safety systems are satisfied," Sisko pressed, "can the probe detonate then?"

"Yes, but it's not a guarantee."

"I don't understand."

"There are at least two scenarios in which the probe won't detonate, even though all safety systems are deactivated and even though the command to detonate is received. One scenario is fairly common, the other is very rare."

"What's the common one?"

"The probe has to be primed before it can detonate," O'Brien explained, as he took a quick look at the tasks on the checklist. "After the probe is launched and positioned, and after the ship is maneuvered into a place to take readings, the probe is given the command to detonate. But if the striker were simply to strike the core, no detonation would occur. That is because the core is essentially in a non-explosive state until just before detonation. What the probe does is it 'primes' the core, getting it ready to explode when struck. The unclassified materials say that the core is subjected to shaped electromagnetic fields to arrange the core's molecules from a chaotic, non-explosive state to an ordered, volatile state. The exact details are kept secret, of course. We know that priming takes about three to five seconds. And we also know this: it doesn't always work."

Sisko raised an eyebrow. "The core doesn't always get primed?"

"That's right. In about one out of every eight probes, there is an 'FTP,' a failure to prime. And if you get an FTP, then the probe is useless, at least temporarily. After an FTP, the probe detects that it didn't prime, so it automatically sends a message to that effect to Probe Control. The probe then assesses its position relative to the ship and plots a course out of the planet's atmosphere. Apparently it takes the probe quite a bit more time to come back up than it did to go down. The ship has to go retrieve the probe with a special retrieval shuttlecraft, after the probe gets itself out of the atmosphere. FTP's are big pains in the arse, if you'll pardon the expression. And apparently, there is no way around FTP's. It's not a problem with the priming apparatus; every so often, the molecules just by chance get arranged in an order that they won't explode. Supposedly, the physics of the situation is that one out of eight probes won't prime, no matter what you do."

Dax frowned. "So, if you wanted to kill yourself and all your shipmates, and you figured out a way to defeat all of the safety systems that would prevent you from killing yourself and all your shipmates, you'd still have a one-out-of-eight chance of failing?"

"That's right. Chances are, you'd succeed, if 'succeed' is the right word. But blind luck might intervene and the probe might not prime."

Sisko asked: "And a probe that fails to prime is a dud, it's useless?"

"Well, not exactly. A probe that has failed to prime can be reset. If a probe fails to prime, the authorization to detonate is rescinded and the retrieval shuttlecraft is dispatched to go get it. An unexploded probe is not permitted to simply be left out in the environment, so it has to be fetched and returned to the Locker. The Locker will not dispense a new probe until the previous probe either detonates or is returned to the Locker."

"So only one probe can be out of the Locker at any time; another security measure."

"Right. The shuttlecraft brings the probe back to a special secure hatch on Observer's hull. The probe is conveyed from that hatch to this receptacle." O'Brien pointed to a slot in a wall. "And from there, the probe goes back to the bench. Once the probe is on the bench, the probe team members in the Bay reinsert the mechanical safeties, and the crane returns the probe to the Locker. Once the probe is back in the Locker, a new probe can be dispensed, and this tedious preparation procedure begins all over again. Meanwhile, the FTP probe undergoes an automatic resetting process inside the Locker. The probe gets refueled, too. Resetting takes about nine hours, I think. But then the probe is like new."

"It still might FTP, again, though?'

"Oh, sure. But it is no more likely to fail to prime than any other probe."

The computer declared, "Scan complete. Probe checklist satisfied. Remove phase buffer deactivator."

Sisko ignored the computer's notification. "What's the other scenario where the safety systems are deactivated yet the probe won't detonate, the scenario that's really rare?"

"The probe might, at the last second, detect life, and re-engage the life detection safety system. This scenario is mentioned in the unclassified documents as one of the selling points of the Mapping Project. Detonation in the presence of life is forbidden by the Convention, and so if a life form shows up right before detonation, the probe will not detonate."

"I'm not sure I understand how that might happen," Sisko said. "Surely they scan for life before sending out any probes."

O'Brien took a breath. "Here's the scenario. The ship has scanned the planet and has detected no life. A probe is deployed inside the atmosphere of a gas giant. All safety systems are deactivated except for the life detection system. The life sensor makes a scan and still detects no life, so it generates a 'no life' signal. As a result, a special barrier interposed between the core and the striker is moved out of the way. The detonation command is received. In response, the probe begins to prime itself. In the few seconds before the probe can complete its priming, the life sensor suddenly detects the presence of life, when no life had been detected before. In that case, sir, the barrier is immediately moved back into place between the core and the striker. It happens fast, the barrier can be repositioned in less than a tenth of a second. Then when the striker moves in to strike the primed core, the barrier prevents physical contact between striker and core."

"And there's no detonation."

"That's right. The impact alone is not enough to cause detonation. The core and striker have to actually touch each other. The life system acts as a safeguard right up to the last second. Needless to say, last-second detection of life doesn't happen very often. Probably never has happened."

Again, the computer declared, "Probe checklist satisfied. Remove phase buffer deactivator."

Sisko gestured to O'Brien, and the two of them together maneuvered the cap-like object from the probe. This was a tricky procedure; it certainly explained why there were two members of the probe team on duty in the Bay, instead of one. O'Brien replaced the cap-like object on the wall. O'Brien continued: "Another benefit of the life detection system is that it is supposed to stop detonation of a probe while the probe is inside the ship."

"This time, it apparently didn't work," Sisko observed.

"That's correct, sir, it didn't," O'Brien replied somberly.

"That special barrier, what do we know about it?" Dax asked.

"Not much. Its actual composition and structure and placement within the probe are classified. The unclassified materials suggest, however, that this barrier can be retracted or redeployed like a curtain, and it can move very quickly. If it is indeed a curtain-type structure, it's probably made of standard alloys in a polymeric matrix, like the flexible barriers used in some Starfleet emergency systems. Those barriers have a good track record of reliability, though they can wear out if exposed to some harsh conditions or forces."

"Why a 'curtain?'" Dax wondered. "Why not a solid piece of material?"

"Probably to save space," O'Brien answered. "There's a lot of stuff packed into that probe. The curtain would be collapsible, and a collapsible barrier would make a great deal of sense."

Sisko wanted to make sure he'd understood the process. "So if the probe is in the planet's atmosphere, and the probe has been commanded to explode, and the life sensor detects life, the life detection system replaces the barrier and stops the probe from priming?"

"Actually, that's not quite right, sir. The barrier may be put back in place, but priming isn't stopped. The shaped electromagnetic fields associated with priming are pretty intense and may have some shear forces associated with them, but those fields are only intense in the area of the core, and they aren't harmful to life. So stopping priming isn't a priority, and I'm not sure you could terminate the electromagnetic fields immediately in any event. Chances are that the probe is primed. The barrier doesn't stop the striker from trying to hit the core, either. All the physical interlocks that keep the striker from moving have been deactivated, and re-engaging them might take a second or two. The barrier can move back in place much faster than that. So instead of stopping the parts from moving, what the barrier does is that it prevents the striker from touching the core, and without actual physical contact of striker and core, there cannot be any detonation."

"What happens to the probe, then?"

"Well, if a life form has been detected in the atmosphere of the planet, then I suppose the mapping mission is effectively canceled. It is a serious offense to explode a probe in the presence of living things. If the probe tells Probe Control that life has been detected, the only choice would be to fetch the probe and go home."

"But when the shuttlecraft goes to retrieve the probe, the probe is still primed."

"Yes, sir, it would be."

"And it's already been given an order to detonate, yes?"

"That's right."

"Wouldn't it be rather dangerous to go get a probe that is already primed and trying to detonate?"

"Not really. The detonation command is not persistent, so the probe is not continuously trying to blow itself up. Probe Control is supposed to revoke authorization to detonate immediately, so the detonation command can no longer be executed. The life detection system is preventing the striker from contacting the core. The other automatic safety systems re-engage pretty quickly as the probe lifts itself out of the atmosphere. Then, of course, additional interlocks are reapplied by the probe team here in the Bay, and in the Locker."

"And this primed probe, does it stay primed forever?"

O'Brien thought for a bit. "I don't think so. If I remember right, the probe stays primed for a while, maybe eight or nine hours, but the primed material naturally reverts back to its unordered, unprimed state."

The computer once again declared, "Probe checklist satisfied."

"Let's finish this up. Probe Preparation Bay to Probe Control Station," O'Brien called.

"Probe Control," answered a voice.

"We've completed the checklist, will make probe ready for launch."

"Acknowledged," said the voice. "Launch, deployment and detonation are authorized."

"Very well, Prep Bay out." O'Brien sighed. "So that's basically it. It took us, what, thirty minutes to go through the procedure, but for a skilled probe team acting without interruptions, probe preparation takes about twenty minutes or so. All I have to do is a final review of the checklist, and sign off of on the checklist," he pressed his thumb on a touchpad, "and the rest is automatic." As he spoke, the crane appeared and attached itself to the probe and carried it to a slot near the Locker receptacle, where the probe was swallowed up.

"Strange that the automated system does all the work, but you have to sign off on the checklist," Dax remarked with a grin.

"Yeah," O'Brien smirked. "Officially, I'm supposed to make a visual inspection and evaluate the readings. If anything looks wrong to me, I'm supposed to decline to approve the checklist, reinsert the mechanical safeties, and then this probe gets returned automatically to the Locker, no questions asked, and another probe gets dispensed. I'd be surprised if that ever has happened. I just can't imagine any probe team saying, 'This probe has passed all inspections, but I just don't like the looks of it; so let's re-shelve it and do this whole boring preparation thing all over again.'"

"So the probe is now in the launcher; what happens next?" Dax asked.

O'Brien chuckled. "The folks in the Bay get to go to the restroom or eat their lunches. Their work is done for a while. Once the probe is in the launcher, it is given a final sterilization. Then the Probe Control Station gives the order to launch, and the probe is launched. It proceeds into the atmosphere of the planet at a desired point. Meanwhile, the ship immediately speeds to the location where it will take readings. I understand they call this 'the sprint," because the ship uses a powered orbital trajectory to get itself quickly into the right spot. Getting the probe and the ship into the right positions takes anywhere from twenty minutes to thirty minutes. Then if everything goes well, the probe is given the authorization to detonate, and then the command to detonate, and it detonates, and the ship is in position to detect the Upsilon Radiation and collect the readings. And then, the officers in the Bay have to get another probe and prepare it."

Dax looked around the Bay. "So each probe takes about fifty minutes from Locker to detonation?"

"Probably less than that," O'Brien smiled, "if you know what you're doing. The Observer people certainly knew what they were doing. They probably were able to prepare, launch and detonate one probe every forty-five minutes or so."

"Chief, I have a hypothetical for you," Sisko intoned. "Suppose we were aboard the Observer, and we came under attack by a ruthless enemy. All of our lives were at stake. No, it's not just our lives that are at stake, it's the safety of the entire quadrant at stake! But none of our weapons function."

O'Brien knew where the hypothetical was going. "And our only possible weapon is a probe."

"Yes. Could you rig it so that we could get a probe to explode near the enemy?"

O'Brien looked Sisko in the eyes. "If it were up to me, sir, the quadrant would be doomed, because I have no idea how to do it."

"But all you'd have to do is make the striker hit the core," Dax interjected.

O'Brien laughed. "Easier said than done. This simulation is a good teaching tool but it is amazing what it doesn't teach. I have no idea exactly where the core and striker are, or how big they are, or what they look like, or what the internal guards and barriers look like. I know next to nothing about the inner layout of a probe, and I don't have the first clue as to what I'd need to do to get the thing to explode, or how I'd go about doing it. If I did anything to try to open the probe, it would detect my tampering and immediately break its seals, causing all of its components to become permanently inert."

They stood silent for a few seconds.

Dax was feeling a little overwhelmed. "This system is very complicated. How many security and safety systems are there altogether? Hundreds? It's going to be difficult for us to sort through all of the safety systems."

"Maybe not," Sisko said. "Think about it. These probes do explode. The purpose of this preparation is to deactivate most, but not all, of the safety systems, so the probe can explode, right? In fact, the probe is supposed to explode, but only under the proper conditions and in the right place. Well. Maybe we don't need to concern ourselves with all of the safety systems. It seems to me that we need to be mainly concerned with the safety systems that are still active when the probe leaves the Preparation Bay."

O'Brien summarized, "When the probe is ready for launch, all safety systems have been deactivated, with five exceptions. The safety systems that cannot be deactivated by Bay personnel are: one, gravitational gradient; two, life; three, environment; four, coded authorization to detonate; and five, actual command to detonate, which causes the probe to prime and explode."

"Six, failure to prime?" Dax added.

"Not really a safety system. More of an enormous annoyance."

"Okay," Sisko drawled. "Let's take them one at a time. Is there any way someone could, say, trick the gravitational gradient system?"

O'Brien grinned. "There might be. You could modulate a graviton stream, aimed from the top of the probe to the bottom. That might cause the sensor to register that it's physically closer to a gas giant than it actually is. You might even be able to do that with a tricorder that has a graviton emitter. I think some tricorders used by geologists have them. I don't see such a tricorder here in the Bay, but I'd bet Observer has a geologist's tricorder on board. Every ship in the fleet has at least one, I think."

"All right, good," Sisko said. "You'll have to verify it, Chief, but for the time being, let's assume for that the gravitational gradient safety system can be deactivated. And let's further assume that the people working at the Probe Control Station issue the detonation authorization code, and the command to detonate."

Dax raised her eyebrows. "That's a rather significant assumption, Benjamin. Can they do that? Perhaps even more to the point, why would they do that?"

"For right now, let's only assume that the people working at the Probe Control Station are able to issue the detonation authorization code and the command to detonate, and that they do so for reasons that we cannot now fathom."

"We'd be left with just two of the five safety systems," Dax said, still unhappy with the assumption. "Environmental and life."

Sisko turned to O'Brien. "How about tricking those final two safety systems into deactivating?"

O'Brien looked around the Bay. He was again about to say it would be impossible, and again caught himself. "It'd be difficult. Presumably, the environmental sensor checks the environment to see whether it is consistent with that of a gas giant. It probably checks the atmosphere and pressure, maybe the temperature as well. If this probe has the same kind of environmental sensors that are deployed throughout the Federation, then I'm not sure you'd be able to fool them, at least not with the equipment in this Bay. You might be able to fake the environment if you had some special instruments, but that would be equipment that Observer almost certainly did not have. The life sensor is probably even harder to fool than the environmental sensor." O'Brien sighed. "Let me think about that problem for a bit."

"Dax, you think about that, too." Sisko ordered. "And so will I. I'm starting to suspect that it may be possible to understand how someone could have caused this explosion."

O'Brien was less optimistic. "Sir, there may be only two systems standing in the way, but they are going to be very hard to defeat; especially the life system. Life sensors are used in Federation applications all over the quadrant. They're used in secured facilities, living quarters, transporters, science installations, airlock systems, science probes, screening stations, all over. We even have had several installed here in Deep Space Nine. They are very robust, have excellent performance records, and are considered to be highly reliable. In fact, I'm not aware of a life sensor ever saying that there was no life in proximity, when in fact there was."

"But these sensors don't detect all life, do they, Chief?" Dax asked.

"I'm not totally certain, but I believe proto-life is not detected at all," O'Brien said, "and life sensors don't recognize genetic fragments or viruses as living. I don't think single-cell forms count as 'life,' though most multi-cellular forms do. So, I'm not completely sure about what exactly what will and will not trigger this sensor into saying that life is present or absent. But I can say this with confidence: a multi-cellular organism like a Human Being, standing less than two meters away, that is a life form that will be detected. And as far as I know, no one has ever figured out how to spoof a life sensor into detecting lifelessness when a person is standing right next to it."

"Check into that, Chief," said Sisko. "That may be one of the keys to figuring out what happened."