The cause of the chirping sound needs to be found, and fixed. From your email, since it's still chirping even when the power is out, the device chirping has a battery.
Because of room acoustics, chirping sounds aren't easy to find. Almost no one is going to be able to tell which direction the chirping sound is coming from, until getting the ear within a foot or so (about half a meter).
The way to find it, though, is to walk around and get close to possible sources of sound, like the furnace or the sump pump. With this kind of chirping, everything is suspect until it has been verified that the source of the chirp is somewhere else.
Check out the furnace, it could be high on the furnace or low on the furnace (stand on your tip-toes, crouch down). Check out the hot water heater, the lawn sprinkler system, the security system, the lights (yes, even the lights), the Wi-Fi, the main electrical box, the air conditioner, even the wall outlets. The chirping is annoying, spend some time closely listening to everything. Until you listen closely and can verify that something isn't making the sound, check it out.
The smoke alarms might be connected together, recheck each one by standing on a short ladder getting your ear within a foot or so (half a meter).
Also, consider the possibility that a smoke alarm that has a battery was disconnected and has fallen under something.
Keep in mind, I can't tell where the chirp comes from without getting really close and listening for a loud chirp; that means that you can't tell where the chirp comes from without getting really close and listening for a loud chirp.
If you walk around, get close to everything, listen closely to everything, you'll find it.
Douglas Krantz
