This project shows how turn ATtiny13 with sound detector module into smart Clap Clap Switch. The project has been designed to react on only double claps (clap clap – ON, clap clap – OFF). So, how it works? There is one pin for a MIC (digital output from sound detector module) and one pin for a LED (to show on/off cases). External interrupt (INT0) has been used to check microphone state. In the main loop there is an algorithm which take care of processes of detecting claps, counters, resetting states and toggling the LED. The user of this smart clap-clap switch has a wide timeframe between first and second clap. In my opinion, It’s enough of time for a double clap but feel free to experiment with other values! The single clap / noises should not affect the process of double-clap detecting (what was the goal!). This project can be easly extended by adding extra components like for example relay to control high voltage devices.