I have a hardwired smoke detector that is old and outdated, that I'd
like to switch with a new unit. The only problem is that I can't
shut
off the power to the alarm before I disconnect it and reconnect the
new one. I'm going to have to do the take-down and installation
while
the power is LIVE.

I live in a high-rise apartment building and the smoke detector is
powered not by my unit's individual power, but off of a line brought
in from a common hallway. There is no way to cut power to the smoke
detector without cutting power to all the lights in the common
hallway, which is impossible.


So, how can I safely (or as safely as possible) change this detector
with a new one? If I don't touch certain wires together, will I be
OK? What are the chances I would get shocked?


I know your first inclination will be to tell me to get the circuit
turned off or call an electrician, but please (at least
hypothetically) assume that neither of those options are possible.