On Tue, 18 Jan 2011 13:06:02 -0700, Tony Hwang
wrote:

First of all if the alarm unit is more than 7 years old, replacing it is
better idea. I just did that, all our units are replaced with dual
sensing ones(smoke, flame=temp.) and they are all hard wired in daisy
chain with back up batteries. If it is chirping better find out why ASAP.

It chirps because the battery is going weak. Replace the battery, test
the alarm and put the ladder away.

My system is interconnected wiring. They don't chirp because of the
power wire.