After hiring 3 separate electricians and replacing all smoke detectors twice, the false alarm was coming from the carbon monoxide detector. It never indicated anything was wrong (eg low battery, etc). The alarm was not a quick sound (as indicated on the product), but instead was a constant sound that would go off at different intervals, having the exact same sound as the "test" alert on the fire detectors (which is why I started there first). The fire department had also been called out twice and this last time they discovered that the CO detector was the problem. One fireman said he had one exactly like this that he had to throw out because of false alarms.