OTOH, I wasn't just asking about the narrative function that you want the trapped lock to serve; also there's the in-game reason(s) that the guild masters would have designed it and put it there. Do only the very few top lieutenants know it's there? Does every guild member know how to use these?
What happens if your PCs just stake out the door and make their way in behind some n00b guildie? What if a PC tries it, gets their hand lopped off, and now there's a rotting hand in the mechanism making it unworkable for the next legitimate user?