Ultra-Sonic Sensor

Ultrasonic sensors are designed to provide intrusion detection of vehicles fitted with sliding windows (as apposed to wind-up) and utilities fitted with canopies. The ultrasonic principle works approximately the same as police radar. A transmitter produces ultra high frequency sound waves which bounce off all surfaces inside the car. A receiver then picks up the reflected sound waves and sends a trigger signal to the connected alarm when a change in the shape of the echo is detected.

Ultrasonic sensors require a rigid, stable perimeter with no air movement, i.e. convertibles will not reflect sound waves and soft-top roof's will move when battered by wind.

ULTRA-SONIC THEORY

Sound pressure waves are transmitted into vehicle by the aptly named transmit head. Frequencies around the 40KHz band ensure the transmissions can not be heard by the human ear.

The sound waves travel through the air within the vehicle cabin and bounce back off all surfaces. Any change in the shape of the surfaces is treated as an intrusion and the sensor triggers the alarm.

Ultrasonic sensors are not suitable for soft-top vehicles and convertibles. Wind blowing through the cabin or wind rustling the soft-top will cause false alarms.

Ultrasonic sensors will not detect movement behind objects blocking the sound waves (i.e. front seats).

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