Air Theremin is a browser-based musical instrument that lets users play a virtual theremin using hand gestures captured by a webcam or smartphone gyroscope.

To play, users position their hands in front of the camera. Spreading hands apart increases volume, raising them adjusts pitch, leaning back softens tone, and bringing palms together silences the sound. A standard laptop webcam works just as well as a phone camera.

On smartphones, users can alternatively use the device's gyroscope. Tilting left or right controls volume, while forward and backward tilts adjust pitch. The full range of motion stays within the phone's frame, and tilting the marker outside the frame cuts the sound entirely. When neither sensor nor camera is available, the mouse can control the theremin.

Upon pressing START, the application calibrates automatically. On phones, users should hold the device steadily during initialization to ensure proper calibration to their grip.

The project was featured on Hacker News, highlighting its innovative approach to gesture-controlled music creation in the browser without requiring additional hardware.