How to use it
- Plug in stereo headphones.
- Press Test left / right: left ear first, then right.
- Pick a speed and press Start.
How the tool works
This free browser tool plays alternating left–right sound, with an optional moving light, so that an EMDR-trained clinician can run bilateral stimulation (BLS) during a session. It needs no account and no download. Auditory BLS needs no dedicated hardware: a computer or phone and a pair of stereo headphones are enough.
Before the first set
Put on stereo headphones and press Test left / right. You should hear the left ear first, then the right. If both ears sound the same, the audio is being mixed to mono and the alternation is lost. Check the headphones and the device’s accessibility settings, then test again.
Settings
- Speed: 15 steps. Step 1 is 1.25 seconds per side (24 passes per minute); step 15 is 0.20 seconds per side (150 passes per minute). The table below lists some of the steps.
- Volume: 1 to 20. Keep it moderate over long sets.
- Tone: High, Mid or Low.
- Visual: Light bar, Sphere or Dot, or Off for sound only. You can also choose the colour (Amber, White, Teal, Lavender or Green) and the size (S, M or L).
- Stop automatically: after 12, 18, 24, 30 or 40 passes, or Off.
- Dark background: switches the stage between a light and a dark background.
During a set
Press Start or the space bar. The counters show the passes, the length of the current set and the session time; Reset counters sets them back to zero. The full screen button (or F) enlarges the stage. While a set is running or in full screen, the up and down arrow keys change the speed, the left and right arrow keys change the volume, and 1, 2, 3 select the tone.
A set stops by itself if the tab goes to the background or another app or call takes over the audio, because browsers slow down background tabs and the beats would become uneven. Keep this tab in front.
Saving and sharing your settings
Your choices are remembered in this browser. Copy settings link creates a web address that restores the same speed, volume, tone, visual, colour, size, background and automatic stop in any browser, for example on a second device.
Online sessions and the app
Video platforms often reduce shared audio to mono. If you use the browser tool online, turn on stereo or original sound and test left and right with the client first. The EMDR Mobile app for therapists adds offline face-to-face sessions and online sessions in which the stimulus plays on the client’s own device while you control it from yours. This tool is for clinicians trained in EMDR, used within a session; it is not a self-help program.
Online sessions (Zoom, Teams, Meet)
Video platforms usually mix shared audio down to mono, which removes the left–right alternation. Turn on stereo or original sound and run the left / right test with your client first. In the EMDR Mobile app the stimulus plays on the client’s own device, so the call cannot affect it.
Speed table
| Speed | Per side | Passes / min | 24-pass set |
|---|---|---|---|
| 1 | 1.25 s | 24 | 60 s |
| 4 | 1.03 s | 29 | 49 s |
| 7 | 0.80 s | 38 | 38 s |
| 10 | 0.58 s | 52 | 28 s |
| 13 | 0.35 s | 86 | 17 s |
| 15 | 0.20 s | 150 | 10 s |
No sound, or it stops?
- Both ears sound the same: mono audio is on. Check the headphones and the device’s accessibility settings.
- It stops when the tab goes to the background. Keep this tab in front.
- iPhone: check the silent switch.
Safety and privacy
- Photosensitive epilepsy: set Visual to Off and use audio only.
- Everything runs in your browser. Nothing about the session is sent to our servers.