Car alarm & dashboard lights came on

I have a 2009 Prius with ~103k miles. Tonight, the some kind of alarm on it went off at random. It's not the same alarm as the panic alarm, closer to the horn continuously honking by itself. This was going on for over half an hour before I realized it was coming from my car.

I went outside, opened the door, turned on the car, and the triangle with exclamation, ABS, VDC, check engine and another exclamation light were flashing. I then tried turning off the car, but the power button wouldn't turn off, the check engine light came on, and I couldn't remove the key. After pushing the power button a few times, I was finally able to remove the key. But now I can't lock the car doors with the fob and the door lock button in the car isn't working. I have to manually lock the car.

Does anyone have any idea what could possibly be wrong?

The 12v battery was changed only a few of months ago and inspection/oil change was done just 2 months ago. Any help would be appreciated.