[Superman]

My sister's old, decrepit Honda Civic was parked behind my house (she's borrowing my truck). It has/had an alarm system that has been mostly disabled, but a light on the dash flashes. Today, I noticed somebody had been in the car (nothing of value was there) and the car's electrical system is not working. Battery is perhaps dead, but I don't know that.

What do lowlifes do to disable a car's electrical system? What happened?