I have three smoke alarms in my house (First Alert). They are wired into the house AC, but have battery backup. They are also wired to communicate with each other. One, the one causing the noise, is also a CO detector. In the last few weeks one of them has started giving me a single beep (let's call that E) or a triple beep (let's call that S), in the middle of the night for no reason. E is a signal to replace the battery, per the manual, although it should be doing it every hour, in that case. At first, I dutifully changed the battery (three nights in a row). S means smoke, but in that case it would be louder & continue until manually reset. There is no smoke. In fact, it DOES NOT go off when the neighbor's BBQ scent drifts through my house.
Finally called the electrician who installed them. The first time he came out, he said they were all old enough to be replaced & charged me a lot to do so. He's been out twice since, because the problem continued, always at night. The only thing he does is replace the offending unit (for free). There is no latch light on any of the three, so no clue which one started the fracas.
What gives!!??!! I'm losing sleep & the dogs are going nuts. Sometimes it triggers a dog fight.