D is for Deadbolt
Deadbolt: a lock bolt that is moved by the turning of a knob or key rather than by spring action.
…
There were things that Naru didn't yearn for – human contact being one of them. He liked solitude, but there were some people that he had begun not minding when they were around. People that could hold intelligent conversation, which he preferred in humans.
Those were the people that he had to be wary about. The ones that had managed to worm their way past his deadbolt. Because once they were there, he couldn't get them back out.
But he made sure they never knew how vulnerable he was, because that could wreak havoc that he would rather not deal with.