Clap Chrono is a classique StopWatch which determine a time, but he has a big particularity.
You Start and Pause the Chrono by clapping your hands.
Clap one time start the chrono, clap again pause, clap again resume ... the reset button stop completely the Watch en reset all time.
An Easy way for Chronometer your sport, a distance with a clap or something like this.
Also work with headset.
The sound is analyzed to differentiate ambient sound and clap.