That the battery in your car is low and needs to be charged
no it doesn't if the door is opened when its ON it makes a circuit and starts the car alarm
If you set the alarm (i.e. lock the car) and then disconnect the battery, the alarm will go off. If you disconnect the battery when the alarm is not set (i.e. when the car is unlocked) the alarm will not go off. (So don't try to nick a locked one).
Disarm the alarm before removing the battery.
sounds like the battery short-circuited.
Car alarms normally work on the battery that starts the car.
Insert the ignition key into the ignition and turn it to on, the alarm should shut off.
Car alarm in Lexus ES300 started going off at random when car was parked, not running. I changed the key fob battery (flat watch battery) with a new battery and it fixed the problem.
You can get a car alarm that uses it's own battery so wont drain the car.
unplug the battery, this will reset the car with the alarm disabled
if you did disconnect the alarm, it wouldn't let you start the car because of the immboliser
It runs off the car's battery.
Usually a flashing red light on the dashboard when the car is off indicates that there is an alarm system active.