Bob Rahe wrote:
Rebecca Webb wrote:
Update.

I showed
http://www.morris.umn.edu/~webbrl/Sm...eDetectorInnar
ds.jpg to an electrician colleague. He said,

"That's a junction box, you ninny. There is no way it can make a
chirping sound. No way, never, nada, zip, no chance, can't happen.

"Your ears are deceiving you. It must be a nearby detector you're
...

During a power failure a while back we had something like this
problem. Chirping from what we THOUGHT was one of the hardwired smoke
detectors. After pulling a couple with no luck finally found it. It
was a CO2 detector that was plugged into the wall near the fireplace.
Those high pitched sounds are REALLY hard for us humans to
echo-locate.

That would probably be a "CO detector"