Before they fought Richard 'Dick' Roman, King of the Leviathans, Sam and Dean Winchester had an idea because they knew Crowley. Crowley would no doubt double cross them again. Even Meg approved of the plan; she'd love to stick it to him any way she could. She would also avoid in any way to be his torture toy because she knew that was going to happen.
"Are you sure these are going to work?" Castiel asked Dean.
"Cas, if Sam says it's going to work, it's going to work," Dean assured him.
"I can't think of an even perfect idea to make sure all of us stay together," Meg replied.
"It's just so we know if any of us gets separated, we know where the others are at," Sam said sheepishly.
"But it's a tracking device inside of us," Meg pointed out. "What could be more brilliant than that?"
"How did you think of this?" Dean asked Sam.
Sam looked at Dean. "It's been something I've been playing around with for years. Trusting Crowley once is enough; trusting him again is foolish."
"And there's no doubt he would double cross again," Dean said. "Let's hope they don't short out on us once we get them in us."
"That won't be a problem," Sam replied. "They have two years worth of life."
"Two years?" Dean asked. "Really? What are we going to do when we don't need them anymore?"
"Take them out," Sam replied. "It's really easy to do."
