since i do this for a living....
most new home systems are AC powered just like any light fixture, and the battery is for back up power in the event of a power outage, however, they are also frequently interlocked so that if one detector alarms, it will signal all the other devices to annunciate as well (snuff out a candle under one, and they all go off, ...so if you headbanger son is rocking it in the basement he won't get trapped in a fire by not hearing a detector on another floor or room) a dead battery should only make that detector chirp.
possibly a detector got fried and is sending a falsh alarm signal to al lthe others - you would have to track down the bad one by trail and error, and replace it. - my guess?
"I really started paying attention to cars was when they came out with the Nissan Z, the first body. Then I seen the Cherokees, the old square ones, and I was like, “Wow, that’s cool.” Then I seen the Isuzu jeeps and I seen the Wranglers."
-Lotus Cars VP of Global Design