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.

With a standard old HC-SR04 ultrasonic sensor, an audio module and a servo to drive a custom gauge needle he’s made a device which can warn people around you if they’re too close for comfort.

In this mode, you can interface the HC-SR04 ultrasonic ping sensor with a servo motor and the main board (Only some reward tiers include the extra servo motor PCB and servo motor kit).