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 ...

This simple STM setup utilises a piezoelectric actuator constructed by deliberately cutting a piezo speaker into four quadrants. With individual drive wires attached to the four quadrants.

Piezoelectric crystals are a class of materials that exhibit a unique property called piezoelectricity. These crystals generate an electrical charge when subjected to mechanical stress or strain, and ...