It's very windy, also blew out candles and thought that caused hard-wired, battery backup smoke detectors to go off - all 9 of them simultaneously at midnight. Fanning with air did nothing. After 20 minutes and no reason discovered we pulled the batteries for a few minutes then put them back in. so far - quiet! If the battery in one unit is bad will it set off the system as a full fire alert? Our other ones just chirped at the affected unit if the battery needed changed, it didn't trip the whole house!

1 likely sensed something or false alarmed, triggering the rest as they are interconnected.
A red light on a detector may tell which triggered them.