The treat in question is detected by an SR-04 ultrasonic distance sensor connected to an Arduino Nano. All in all this was a highly successful build as far as neighborhood entertainment value goes.

Arduino and ESP8266 project measuring distance with ultrasonic sensor, connecting to AWS IoT and Arduino IoT Cloud for remote monitoring and control.

An ultrasonic sensor works by emitting high-frequency sound waves (ultrasonic pulses) and measuring the time it takes for the waves to bounce back after hitting an object. The sensor then calculates ...

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