Every friday in work, at around half past 10, the fire alarm is tested. This morning when it went off at 10:28, everyone thought they were simply 2 minutes early and stayed in the office. After about a minute the alarm was still sounding so we decided an office evacuation might be a good idea. At least it wasn't raining.
It turned out to be a problem with the alarm panel (they couldn't get the alarm to switch off) rather than a 'real' incident.