As shared by Kidde - maker of Smoke and Carbon Monoxide Alarms for the home.
It's a sound many homeowners have heard: the 3 a.m. alarm chirp. Why does it happen? Well, it's a simple matter of the battery's charge level and a home's air temperature.
As a smoke alarm's battery nears the end of its life, the amount of power it produces causes an internal resistance. A drop in room temperature increases this resistance, which may impact the battery's ability to deliver the power necessary to operate the unit in an alarm situation.
This battery characteristic can cause a smoke alarm to enter the low battery chirp mode when air temperatures drop. Most homes are the coolest between 2 a.m. and 6 a.m. That's why the alarm may sound a low-battery chirp in the middle of the night, and then stop when the home warms up a few degrees.