Most car alarms on the market today are connected to the battery. This is because the battery provides a constant source of power, even when the car is turned off. Some older car alarms may be connected to the ignition system, but this is not as common anymore. The reason for this is that if the alarm is accidentally set off, it will drain the battery and possibly cause other problems. By connecting it to the battery, you can be sure that the alarm will always have power and be ready to go when you need it.