Car alarms with pressure sensor

Volume sensor

— the volume sensor monitors the space and reacts to changes in the set of objects within the coverage area — primarily to the appearance of new objects. Such sensors are most often made internal — they provide monitoring of the situation in the cabin and complement the perimeter security system, reacting to intrusion even if the attacker was able to bypass the limit switches and shock / vibration sensors. There are also external sensors that monitor the approach of strangers to the car and give a warning signal. Both those and others, usually, work at the expense of ultrasonic signals, which allow you to "see" the protected volume.