It runs on mains power and uses a 100dB piezo buzzer for ear-splitting effectiveness to alert [Adam] whenever the freezer is at 32°F/0°C or above. If the Arduino loses sight of the DHT22 ...

However, [Billy] figured out a way to build them on the cheap. The build starts with a common piezoelectric buzzer. It’s torn down and the extraneous circuitry inside is removed. The piezo ...