i had a hardwired smoke alarm go off repeatedly one night at my old building (crappy landlord). in the past, random alarms were caused literally by a spider sitting on the sensor. a few thwacks and out it crawled. the last time however, it was finally all the humidity that must have shorted out something in a different detector in the back. i called the firedepartment twice (once to respond to the alarm, the second time to have them back to disconnect the thing cause it wouldn't turn off and they found nothing wrong). said they'd contact the landlord. never knew if they did - never saw the landlord fix anything & i moved out of there asap that year. my guess involved either the squirrels or mice in the crawlspace snacking on the tasty wires.

anyway, just thought you might want to hear that you're not alone, and sometimes the alarm has just become a spider's home. :p