Flaky smoke detector?
The system went off for appx. 20 seconds, then turned off for 10 or so then back on. The second time it went off I pulled the detector in the upstairs hallway (the green light was flashing steadily) and the alarm immediately turned off. I didn't realize this but apparently a steady flashing light on the units means they have stored alarms (since the last reset), a good troubleshooting tool I guess. I replaced the battery, reset the alarm (by pressing the test button), reinstalled it and it's been fine since. I also pulled the alarm on the 1st floor which was also flashing steady and replaced the battery, although that's the alarm that always goes off when stuff is burning in the kitchen.
FWIW, the units are all 10 years old or so; the 2nd floor unit I pulled down to replace the battery had a manuf date of 03/05. I'd been thinking of replacing them due to yellowing anyway.
Looking online it seems old detectors can be flaky - not work at all or work "too" well (as is my case). Just wondering if this is prevalent at all?