One is a backup and sounds an alarm when it is switched on ... This one uses a single ultrasonic rangefinder which we think is much simpler. It’s accurate to about 1cm and is simple to use ...

One is a backup and sounds an alarm when it is switched on ... This one uses a single ultrasonic rangefinder which we think is much simpler. It’s accurate to about 1cm and is simple to use ...

An ultrasonic emergency notification/communication system The receiver decodes the modulated ultrasonic signal emitted by the PAT transmitter An alarm contact ...