Darn glad I had read this thread, in advance! Just happened to me.

Remote wouldn't work (while parked at work). Was moving fast: unlocked the door and the ear-splitting alarm sounded. Forgot to NOT try the key in the ignition -- did, and wouldn't silence the alarm.

Got the 10mm wrench out of the console box (thanks for the warning to put one there!), popped the hood, and disconnected the negative cable of the battery. Alarm turned off, briefly, then reactivated (now sounding due to disconnected battery?).

Tried the key and remote again, but siren wouldn't turn off. Scratched my head for 10 or so seconds, then reattached the battery cable. Siren turned off!

Closed hood and started the car normally. When got home, the remote's unlock worked again, but haven't tried locking. Will check the remote and main batteries this evening.

Not a great way to start the weekend ...