Chirping noise every 36 seconds round the clodk
I removed the hard wired Firex FX1014 and all 4 battery smoke detectors and still heard the chirping. Turns out in my case post BV00160 had the answer. They indicated that there was a CO2 sensor in the area. Sure enough, that was it — turns out it was a weak battery. Now I just need to re-install all the smoke alarms.