Generally, OEM alarms monitor the doors and trunk/hatch for unauthorized entry. On some vehicles this is done through pin switches, mercury switches, or microswitches integrated into the latch. On others, the doorlock mechanisms have switches built into them. Some OEM alarms additionally will trigger if the hood is opened, or if the ignition is turned on. A few systems have a shock sensor which will trigger upon a significant impact to the vehicle's body, such as window glass being broken. Motion sensors monitoring the vehicle's interior are installed in some higher end models.