At about 3am this morning, one of my smoke detectors started to give off a chirp -- the 'maybe my battery is dead, maybe I'm dirty' chirp.

We managed to more or less sleep through it. By the time we got up in the morning, no more chirps. I'm sure it's waiting for us to be fast asleep again.

I've been through this before. These are all, by the way, wired detectors. it's their backup batteries that they complain of.

A few weeks ago, in the hopes of heading all of this off, I double-checked that all the batteries were recent, and I replaced all the remaining 10-year-old detectors with new ones.

**UPDATE**

3:30AM this morning. *Beep* \*Beep\*

Take a walk around. It is *not* evident which one is making the noise. Reach a conclusion. Pull one down. Back to bed.

A few moments later: *Beep* \*Beep\*

Out of bed again, but it refuses to beep while I'm standing there.

There are not alarm beeps, these are battery beeps.

Turn up the thermostats to daytime. Beeping stops.

Any suggestions?