The alarm for an opened exterior door was sounding as I entered the building this morning. According to the police dispatcher, security thought they saw someone entering the building and opened an exterior door to follow. This set off the alarm and they could not shut it off. The alarm stopped at 7:19 A.M.
The fire door in the reference stair well was ajar, thus the alarm. I pulled it shut (it was open an inch or so) and that silenced the building alarm.