Inside [Klaus]’ device is an Arduino Uno, an HC-SR04 ultrasonic distance sensor, ... He’d have got 3-4 sensors and a little LED/beep display to be placed on his dash. Report comment. Reply.

Instead, it relies on an ultrasonic distance sensor to detect a hand (or foot) waved in front of the door. An Arduino Leonardo runs the show, sounding a buzzer when the ultrasonic sensor is triggered.