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
hearing. [The bedroom detector is only about 10 feet away.] Try doing
some more trouble-shooting, beginning with pulling down the bedroom
detector to see if that stops the chirping."

Now, incorporating the info I've gained from y'all, when I look at the
bedroom detector, if it IS the problem, chances are it will be blinking
or illuminating in some manner different from the others, right? I
mean, assuming the others are okay.

RW