Did you hear San Francisco's Outdoor Public Warning System let loose with its alarming howl late Saturday night or early Sunday morning? Well, it obviously wasn't end times, as we're all still here writing for/reading this site today (something that one hopes the apocalypse would get us out of doing). So what was it? That's a great question, and one SF's Department of Emergency Management is still trying to answer.

Sirens in the areas of Bernal Heights, Noe Valley, Hunters Point, the Bayview, and City Hall first went off at 11 p.m. on Saturday night. The alarms, which most San Franciscans are used to hearing only at noon on Tuesdays, are placed all over the city (here's a map). It appears that only some of the sirens went off, as opposed to the coordinated 15-second tone we hear during the Tuesday tests, but it was enough that 911 and 311 lines were flooded, DEM spokesperson Francis Zamora said.

The alarms went off again at 5 a.m. Sunday, prompting even more calls, Zamora says. He says that there was no known emergency that would have triggered either of the alarms.

The alarms were taken offline on Sunday afternoon for tests to determine the cause of the unintentional discharges, but the results of the tests are still "under review."

According to the DEM's website, in the event of an actual emergency, a "15 second alert tone will sound repeatedly for 5 minutes," during which residents should "listen for possible voice announcements" and "turn on the radio or television, (such as KCBS 740AM, KQED 88.5 FM) for important information provided by the city."

The DEM says they'll also notify residents via their text and email alert system, for which people can register at http://www.alertsf.org. However, anyone who's on the Alert SF list knows that notifications are inconsistent, often arriving hours after an event. The DEM does appear to be more consistent in its use of Twitter for alerts (they're @sf_emergency), so that might be a better bet.