Inside [Klaus]’ device is an Arduino Uno, an HC-SR04 ultrasonic distance sensor, and an Adafruit Wave Shield.

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.

This one is an unusual smart home project, potentially - how to monitor a fish tank’s health with an AI-enabled ultrasonic sensor system. The detailed project is highlighted on Hackser.io and features ...