Theremin I/O vs Index Theremin
Price, ratings, monetisation and update history for both apps, side by side — with what reviewers say about each.
Theremin I/O
Transform your iPhone into a touchless musical instrument using your camera and flash. Control sound generation by hand proximity, with options for scales, sound presets, and effects. An in-app purchase enables MIDI controller functionality.
- Touchless instrument control via camera
- Adjustable scales and harmony quantization
- Multiple sound presets with effects
- MIDI controller functionality (in-app purchase)
- Interactive tutorial overlay
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Play with light – Theremin I/O turns your iPhone into a touchless music instrument. It uses your camera and flash to measure the distance to your hand, this signal is then processed by a synthesizer to generate a tone. Features: • Old-school synthesizer • Constrain input to scales (harmony quantization) • 8 sound presets with effect controls • 50+ scale presets • Use as a MIDI controller (requires in-app purchase) • Learn fast with the tutorial overlay For more information visit http://theremin.io
Index Theremin
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Theremin is a tiny instrument you play with thin air. Hold up one finger in front of your phone: raise it for higher notes, move it sideways to play louder. That's it, you're playing. Make a fist to stop. A SOUND FOR EVERY MOOD • Theremin: the classic eerie wail • Dusk: a dark, slow, melancholic synth • Aura: an airy, voice-like pad • Glass: a soft, bell-like shimmer • 8-Bit: a video-game square wave ALWAYS IN TUNE Auto-Tune snaps you to a scale (major, minor, pentatonic or every note) in any key. Hard for the robot effect, Smooth for a gentle glide. PLAY A DUET Turn on Duet Mode and each hand becomes its own instrument, with its own sound and settings. TWO FINGERS, TWO JOBS Raise two fingers and your hand switches to a second sound, or turns into a controller for an effect: sweep a Wah, stretch an Echo, speed up a Vibrato. Six effects to play with: Reverb, Pulse, Echo, Wah, Vibrato and Crunch. SAVE YOUR SETUP Presets keep every sound and effect on both hands. Start from one of six, from Classic to Conductor, where one hand plays and the other shapes the sound. MORE TO PLAY WITH • Note Guides show where every note sits on the screen • Volume and octave for each hand • Make a fist to mute without hiding your hand • Portrait or landscape, iPhone and iPad • Works with VoiceOver, Voice Control and Larger Text PRIVATE BY DESIGN Hand tracking happens entirely on your device. Nothing is recorded, uploaded or collected.
Screenshots
Verdict
The clearest difference is price: Index Theremin at Free against Theremin I/O's $2.99. Index Theremin also leads on in-app purchases (none vs 1) and update cadence (every 3 weeks vs every 24 months). Theremin I/O's advantage is iOS requirement (8.0 vs 17.0). On ads and device support there is nothing between them.
Scored on Price · Rating · Positive reviews · Number of ratings · Update frequency · Ads · In-app purchases · Monetization · Best chart rank · Devices · Requires iOS
Index Theremin is free to download; Theremin I/O costs $2.99 up front. Theremin I/O sells 1 one-off in-app purchase. Index Theremin asks for nothing beyond the download.
Theremin I/O ships an update every 24 months, Index Theremin every 3 weeks. Both last shipped on November 6, 2026.
| Parameter | Theremin I/O | Index Theremin |
|---|---|---|
| Price | $2.99 | Free — better |
| Rating | 4.0 (5 ratings) — better | — |
| Positive reviews | 76.9% of reviews | — |
| Number of ratings | 5 — better | — |
| Update frequency | Every 24 months | Every 3 weeks — better |
| Ads | No | No |
| In-app purchases | Yes | No — better |
| Monetization | Paid | — |
| Devices | iPhone, iPod | iPhone, iPad |
| Requires iOS | 8.0 — better | 17.0 |
| Further details — not scored | ||
| Size | 18 MB | 1 MB |
| Age rating | +4 | 4+ |
| Developer | FFFF00 Agents AB | NOAH REMI FINN BESENDORFER STAHLHACKE |
In-app purchases
Theremin I/O
- Network MIDI$5.99
Index Theremin
No in-app purchases









