I have a 3 year old home. The house has seven (7) smoke detectors, four (4) CO detectors, and, in the garage, two (2) heat detectors. All of the units have hard-wired power with battery (9V) back-up, all connected in a single network. The chirping happened about a year ago. I replaced all 13 batteries, tested every unit successfully (when you press a unit's test button, it sounds its own alarm first, then echos the alarm in all other units, then repeats this process, then re-sets. Then every 35-45 seconds (timed check occurred usually every 44 seconds, though sometimes as short an interval as 35 seconds or as long as 45 seconds), one of the units, a unit in an open area between upstairs bedrooms, chirps once. A repeat of the four upstairs alarm units resulted in a more than five (5) minute cessation of the chirping routine. So, I thought the insanity generator had ceased. Not so. It resumed its chirping in 35-45 second intervals. A re-test of EVERY unit proved every unit functions properly, has a connection to the network and the power source, etc. EVERY unit has a brand new 9V battery. Every unit has the battery properly installed (a battery installed backwards results in a shrill alarm immediately - I tested that concept). BRK electronics makes all three (3) types of the alarms in this home network. All 13 units have no dust or cobwebs. Bottom line: ALL the units and the network pass every test any expert or commentator online has mentioned. With so many online entries mentioning that their home smoke/CO/heat sensors/alarms chirp falsely at frequent and random times, it seems that until the home alarm industry can solve this problem, the US citizens will likely die from insanity or suicide before ever facing the risk of smoke or CO. I recommend immediate removal of ALL home smoke/CO/heat sensors/alarms until the industry clearly proves, beyond a doubt that every unit they offer for sale works properly, sells at an economical price, has a simple bypass for a single defective unit (if it decides to start waking the household with a false alarm or battery replacement chirp in the middle of the night), that has a simple (no glue, no more than two screws, a standard plug/pigtail wire connector, etc.) replacement process, and ALL manufacturers follow a STANDARD INSTALLATION PROCESS and STANDARD BATTERY REPLACEMENT PROCESS. Annual (or semi-annual) battery replacement should take no longer than five (5) seconds per unit. Current replacement times, with non-standard battery replacement (ALL from the SAME MANUFACTURER!) from unit to unit, with no clear battery polarity (+/-) indicators -- some have a swing-out compartment, some have a slide-out battery compartment, some have a battery wire harness, some require full cover removal, some require partial cover removal, some have a clip-off battery cover, some have one screw battery covers, some have two or four screw battery covers, some have phillips head screws, some have slot-head screws, all take 1-2 minutes (minimum) per unit for battery replacement. We want the detectors/alarms for the safety of our families, not to support the profit margins of the alarm companies.