There are many forms of input that can be used to control an Arduino or compatible boards, and one of these is sound. This can be used not only for complex signal analysis but also detection of short, sharp sounds such as clapping.
A demonstration of this has been documented by Instructables member YadaP who has created a clap-controlled robot. The output from a microphone sensor module is measured by one of the analogue input pins and once a threshold input as been exceeded, the signal can be interpreted as required. And thus claps can be detected as used with this project.
If you're interested in experimenting with sound and your Arduino or other development board, our Freetronics MIC: microphone and sound module is perfect.
The MIC: contains an integrated dual signal amplifier converts the sound to separate channels for pulse / frequency measurement, and sound volume (pressure) level. Designed to connect straight to an Arduino compatible microcontroller, Analog to Digital converter, or many other circuits. For more information and to order click here.