Firewall

Ok, I just started playing that game but I know what you are talking about. Picking up the key sets off the booby trap so you need to find the fake key to swap it with in order not to spring the trap. You obtain it by finding the dog whistle and using it on the east balcony. One of the dogs that comes when you call will be wearing a shiny collar. Killing the dogs will drop the collar. Examine it and it'll ask you to push the button on it. This small coin-ish thing comes out. Examine it and it'll reveal that it turns into a key but states that it lacks the proper details to be a real one. Use that to swap with the key in the armor room.