A mandatory component of a car alarm is a room sensor. Two types of sensors are used: ultrasonic sensors and microwave sensors.

The ultrasonic sensors remain visible in the room (small "microphones" in the ceiling), but compared to the microwave sensor (remains hidden in the cabin), they give fewer false alarms because the monitored area remains strictly inside the car, and due to the technology, they ensure uniform monitoring along the length of the car.

Light gray sensors
Attached between the plastic of the A-pillar
A strong negative impulse
Compatible with original alarms