On Jan 25, 6:00 pm, wrote:
There's a metal box attached to the side of my smoke alarm box with
what looks like a phone line coming out of it. It travels between the
joists for about 10' before disappearing into the subfloor above. I'd
like to disconnect this box to mount the smoke detector in a new place
(and will reattach then if needed).

PIc is at:http://img89.imageshack.us/img89/8822/img0693st8.jpg

Thanks!

Gawd only knows, from a picture, but it is remotely possible that the
transformer is part of some enhanced alarm system -- possibly powering
a bell or strobe that activates when/if the smoke detector goes off.
Something like that would be used if the previous owner had a handicap.