His binary clock uses an Arduino Duemilanove (which fits perfectly ... A small piezo speaker serves as the alarm buzzer, which should be sufficient to wake up most people, though something bigger ...

It runs on mains power and uses a 100dB piezo buzzer for ear ... If the Arduino loses sight of the DHT22 temperature sensor inside the freezer, then the alarm sounds continuously.

the sensor will detect a drop in light intensity and subsequently activate the buzzer. The alarm only stops when you press the push button connected to the Arduino. For this setup, the program ...