One of the side missions has you steal the voice box for the metal man, but the safe with the voice box in it is trapped.
It would seem that the only way to disable the trap lies in going to the top floor, but there's a couple of guards hanging around, making it difficult to sneak through undetected.
How do I get past the guard undetected?
Best Answer
This is actually the trickiest problem I've faced so far, playing the new Thief.
There's a ventilation shaft in the room next to the safe room, which leads back to the entrance with the stairs. You'll need to go through that shaft and exit it1. Stick close to the shaft entrance, or you'll be spotted by the guard.
Shoot a blunt arrow on the switch, by the staircase leading downstairs; this will turn off the lights and give you a good opportunity to sneak upstairs undetected.
You will obviously raise the guard's suspicion, but at least you won't be detected.
1: You might want to save beforehand.