[notmytarga]

I've had to replace a few of our ten detectors over 7 years. They have a limited life.

You are lucky - yours seem to be ganged correctly. In my last house they were wired but not getting 110V - I pulled them down and checked voltage and resistance and eventually found that the first in the series had a wirenut on the incoming romex and the wire hadn't been stripped - they were never connected! Great inspection by the permit inspector and my prepurchase inspector. In my current home the detectors are getting 110V but they are not connected with three conductor wire so they DO NOT go off together. The house is 10 years old and I suppose that it was a code violation not picked up.

This house also has a too complex security system with intercom and porch cameras etc - but there was no smoke detection on the security system until I added it. Really brainless!!

Someday I want to oversee the construction of my own home - I had fun helping the subs on our pool - and they added spigots, outlets, decking, features to compensate my interest.