The Strange Case of the Chirping Smoke Detector

Perhaps two or three years ago, the smoke detector in the stairwell started chirping (i.e., giving very brief high-pitched sounds) intermittently. I figured it meant the battery was low, so I replaced the battery. The chirping didn't stop, so I removed the battery. The chirping continued for a while but eventually stopped.

Recently, it started chirping again. I had forgotten that I had removed the battery, and supposed that the battery needed to be replaced. I was surprised to see that there was no battery. My guess was that the humid air of summer had somehow activated it and that a fresh battery would take care of it. But the battery didn't stop the chirping, so I disconnected it from the contacts. Now, there's maybe a 1/4 inch gap between the battery and the contacts in the detector so I can reinstall it if I decide I need to. Disconnecting the battery hasn't stopped the chirping, but I think it isn't quite as loud as it was with the battery installed.

So there's still the ongoing mystery: how does a smoke detector without a battery get the power to make sounds, even the sounds that indicate a weak battery. I still wonder if the humidity had anything to do with it. But there's even more. Since I first removed the battery, the detector has continued to give its proper alarm (sustained high-pitched sound) when smoke from overheated cooking fat reached it. It stops when I ventilate the area. Since I had forgotten that I had removed the battery, I wasn't surprised at these alarms until now.

I have a smoke detector which "said" it needed a new battery a couple of years ago, which hasn't had a battery since then but continues to give an alarm when it detects smoke, and which has resumed signaling that the (absent) battery is weak. I wonder if it will stop chirping anytime soon, and if it does will it continue to sound an alarm for smoke.