OffMic

A private voice channel for your team, during your Teams meetings.

Install for Chrome  ·  Install for Firefox

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The problem

You are in a Teams meeting with a client. Your team needs to talk something over, right now, before answering. Today that means switching to another tool, opening a side conversation, or staying quiet and waiting.

The solution

OffMic adds a private voice channel between your teammates, driven by one thing only: your microphone state in Teams.

Teams mic	You talk to	You hear
Muted	your team	your team
Live	the client	your team (on by default)

No extra button to manage, no shortcut to memorize. You mute yourself the way you always do, and that gesture becomes the trigger. Mic muted, I talk to my team. Mic live, I talk to the client.

How it works

OffMic never controls the Teams microphone. It watches it.

1. Detect. A content script observes the Teams web mic button and derives the muted or live state.
2. Capture. An offscreen document opens the microphone alongside Teams.
3. Decide. The outgoing track is enabled only when the connection is up and the Teams mic is muted.

Where the capture and the peer connections live depends on the browser. Chrome hosts them in an offscreen document; Firefox refuses microphone access from an extension background page, so it hosts them in the Teams tab itself. The media code is the same file in both cases, only the host changes.

Voice travels over peer-to-peer WebRTC, in a mesh. It never goes through a server. The signaling server only introduces peers to each other, just long enough to exchange SDP descriptions and ICE candidates. Once the peers are connected, nothing flows through it anymore.

  Alice ◄──────── P2P audio ────────► Bob
     ▲                                 ▲
     └───── SDP / ICE ─────┬───────────┘
                           │
                 signaling server
                 (never any media)

Before you install

• Headphones are mandatory. If your team's voice comes out of your speakers while your Teams mic is live, the client will hear it. No software can fix that.
• Teams web only. A browser extension has no reach into the Teams desktop client.
• Detection depends on the Teams DOM. Microsoft can change its UI and break it. English and French interfaces are recognized, with a polling fallback.
• Chrome and Firefox. Chrome runs the voice channel in an offscreen document, Firefox inside your Teams tab. Same code, one manifest each.
• Up to 5 or 6 people. Beyond that, a peer-to-peer mesh costs too much upstream bandwidth.

Install

OffMic is published on both stores.

Chrome

chromewebstore.google.com/detail/onacjipehnjfchieiakjlofndidcnkod

Firefox

Firefox 115 or newer.

addons.mozilla.org/firefox/addon/offmic

On Chrome, one permission step

Open the popup and click the microphone permission link once. That step matters: the offscreen document has no UI, so it cannot show a permission prompt. Without it, capture fails with NotAllowedError.

On Firefox, nothing to grant

Firefox refuses getUserMedia from an extension background page outright, whatever permission is stored, because there is no browsing context to attach the capture to. So on Firefox the voice channel runs inside your Teams tab instead, as a content script. It captures under the Teams origin, which already holds the microphone permission for your meeting, so there is no second prompt and nothing extra to click.

The consequence is that the Teams tab is the channel. Connect with your meeting open, and if that tab is closed or reloaded the channel stops and the popup says so.

Nothing else to install. The extension already points at a hosted relay, so joining a room is all it takes.

Usage

1. Join your meeting on Teams web.
2. Open the OffMic popup, enter a room name shared with your team, and your own name.
3. Click Connect. The ring in the toolbar icon turns green.
4. Mute your Teams mic to talk to your team, unmute it to talk to the client.

The room name is the only shared secret. Pick one nobody will guess.

The gear icon opens the settings: language, appearance, which microphone and audio output OffMic uses, and the two volumes (your mic, and the team you hear). Everything applies live, without dropping the connection.

Each teammate in the list also carries its own mic toggle and volume slider, so one loud voice can be turned down instead of turning everyone else up. Those are per session: someone who leaves and comes back is back at full volume.

Installation, if you want to host your own relay server

None of this is needed to use OffMic. The store builds already point at a hosted relay, so installing one and joining a room is all it takes. Follow the steps below only if you would rather run the signaling for your team yourself.

Note that pointing at your own relay does not require a clone either: the address is editable straight from the popup, in the store build as much as in a local one.

Requirements

Node.js 18 or newer, and Chrome or Firefox.

1. Clone

git clone https://github.com/Bysimeit/OffMic.git
cd OffMic

There is no build step. A fresh clone already points at the public relay wss://offmic.xeron.be, so you can skip straight to the next section.

To use your own server instead, open extension/config.js and change the one line in it:

const OFFMIC_CONFIG = {
  serverUrl: "wss://relay.example.com"
};

That value is only the default shown on a fresh browser profile. The address is editable in the popup at any time, and what you type there is remembered, so trying another relay never requires touching a file.

2. Load the extension from source

Skip this if you already installed a store build, it works the same against your own relay.

extension/ holds one source tree and two manifests: manifest.json for Chrome, manifest.firefox.json for Firefox. The build script copies the tree into dist/, one folder per browser, with the right manifest in place:

node tools/build-extension.mjs

On Chrome you can also load extension/ directly, since its manifest.json is already the Chrome one.

Chrome

1. Open chrome://extensions
2. Turn on Developer mode
3. Load unpacked, then pick dist/chrome/ (or extension/)
4. Open the popup and click the microphone permission link

Firefox

1. Open about:debugging → This Firefox
2. Load Temporary Add-on, then pick dist/firefox/manifest.json

Being a temporary add-on, it goes away when you restart Firefox.

The last Chrome step matters: the audio runs there in a context with no UI, so it cannot show a permission prompt. You have to grant access once from the dedicated page, otherwise capture fails with NotAllowedError. Firefox captures inside the Teams tab and has nothing to grant.

3. Run the signaling server

cd server
npm install
npm start

The server listens on port 48085, configurable through the PORT environment variable.

A Dockerfile is included in server/ if you would rather run it in a container.

Privacy

• No account, no sign-up, no usage tracking.
• Voice never passes through a server. Media is end-to-end encrypted by WebRTC (DTLS-SRTP) and goes straight from peer to peer.
• The signaling server keeps rooms in memory and writes nothing to disk.
• Your settings stay in your browser's local storage.

The weak spot is not technical, it is acoustic: see the note about headphones above.

License

Released under the GNU Affero General Public License v3.0. See LICENSE.