One of the motivations for this was that the spiders, when very very small, crept into the smoke detector in search of the teeny amount of warmth it put off, and set off the alarm.
When we moved to Massachusetts, we bought a house built in the tail end of the boom (we bought in the spring of 2009), and with some of the problems that tend to happen with boom construction (basically, when everyone has work, newer and/or less reliable workers are employed and the quality of the resulting work isn't as consistently good -- you can tell roughly how the economy is doing by how polite, efficient and accurate the workers at fast food places are; they're fantastic in a bust and it's just not worth the risk during the peak of a boom). The (many many many, like, a dozen) smoke and fire and carbon monoxide alarms had nuisance alarms every few days. It was the first time in my life I was tempted to disable all the alarms. Oh, and they're all interconnected which makes it tricky to figure out which one was going off, because they set each other off.
Anyway. We hired an electrician to fix the problem and he said that that year of fire alarms had a ten percent "bad" rate, thus guaranteeing any house with as many alarms as we had was virtually guaranteed to get one of the troublesome ones. We had them all replaced and there were no further nuisance alarms until a couple nights ago, when shortly after the kids were in bed and A. was probably even asleep, they went off. We got them reset and were searching for online manuals to debug which one was setting the rest off when they went off again. Reset again, and then I went to go stare at their various LEDs, and figured out -- not based on the manual, but just looking at the blink patterns -- it was the one in the master bedroom. R. got it down and, sure enough, there was a spider.
Those noisy spiders.