Wave your hand at a webcam, hear a theremin: browser instrument released

The theremin is an electronic instrument invented in the 1920s by Russian inventor Leon Theremin. Its defining feature is that the player never touches the instrument — pitch and volume are controlled solely by the position of the hands between two antennas. The principle converts changes in the electromagnetic field, caused by the hand moving closer to or farther from the antennas, into sound. This browser version recreates the same experience without physical antennas, instead using the webcam's hand-tracking technology or a smartphone's gyroscope sensor.

How to try it

Where to start

Visiting the project page in a browser brings up a START button at the bottom of the screen. On a laptop, the built-in webcam is used as-is; on a smartphone, the gyroscope sensor is used. In environments with neither, a mouse can be used instead.

Step-by-step instructions

1. After opening the page, choose either GYRO or HANDS from the input mode menu at the top.
2. Press the START button. On a phone, holding the device steady in your normal grip for a moment triggers automatic calibration to match your grip.
3. In HANDS mode, keep both hands inside the camera frame and watch the screen to control the sound. Moving your hands out of frame silences the sound.
4. In GYRO mode, tilting the phone left and right controls volume, while tilting it forward and back controls pitch. If the on-screen marker moves outside the display range, the sound stops.
5. From the waveform menu at the top of the screen, choose a tone from SINE, TRI, WARM, or REED, and toggle reverb, note-snap, and effects such as vibrato, tremolo, and echo on or off.
6. To save a performance, press REC to start recording and PAUSE to pause it.

Who can use it

Anyone with a laptop or smartphone equipped with a webcam can run it directly in a browser with no separate app needed. On desktop setups lacking both, mouse input serves as a substitute.

What you can try

For example, during a spare moment before a video call, you could wave your hands in front of the webcam to improvise a melody, or sit quietly with a smartphone and experiment with pitch using gyro mode. Rocking the device side to side like a seesaw produces vibrato, while tilting it backward darkens the tone and widens the sense of space — the response is immediate enough to make it useful for quick sound sketches.

Editor's view

The theremin's entire appeal has always rested on the novelty of playing an instrument without touching it. A physical theremin requires two metal antennas and analog circuitry, making it a high barrier to enter as a hobby — but this project lowers that barrier to a single webcam. In the past, building a hand-recognition instrument would have required dedicated sensors or specialized hardware; now, a browser's webcam API combined with a hand-tracking model is enough to replicate the same experience. That shift is what this project demonstrates.

For teams in Korea looking to reference a project like this, the key takeaway isn't "faithfully recreating an instrument" but "instant responsiveness." Even if the pitch isn't as precise as a real theremin, if there's no-lag feedback where the sound grows louder the instant hands spread apart, users keep moving their hands. For individual developers or small teams planning webcam-based interactions, spending budget and time on response speed before accuracy tends to boost perceived quality far more.

In the coming weeks, it's likely that derivative projects will emerge from forks of this codebase, extending it from hand tracking to facial expressions or full-body movement. The very format of a browser-based instrument that runs on nothing but a camera makes it an easy invitation for follow-up experiments.