Table of Contents

Firefox OS Tricorder

The following slides are available in this presentation:

Firefox OS Tricorder

Reading Device Sensor Data in JavaScript

Robert Kaiser, "KaiRo" <>
Program Manager, Mozilla QA


What is a Tricorder?

Starfleet Tricorder, 2370

Sensor device as seen on "Star Trek"

Displays whatever data is needed at plot speeds and resolutions.

Firefox OS Tricorder App

Displays data from device sensors as exposed by WebAPIs


Firefox OS Tricorder UI

Tricorder UI description


Position Module

GPS, WiFi/Cell Location

API: Geolocation

Permission: geolocation

Position: Code

  this.watchID = navigator.geolocation.watchPosition(
    function(position) {
      position.coords.latitude / .longitude / .accuracy / ...
    function(error) { ... },
    {enableHighAccuracy: true, maximumAge: 10000, timeout: 60000}


Gravity Module

Accelerometer, Magnetometer

APIs: deviceorientation, devicemotion events

Permissions: ---

Gravity: Code

  window.addEventListener("deviceorientation", this.orientEvent, true);
  window.addEventListener("devicemotion", this.motionEvent, true);

  orientEvent: function(orientData) {
    orientData.alpha / .beta / .gamma (in °)
  motionEvent: function(event) {
    event.accelerationIncludingGravity.x / .y / .z (in m/s²)

  window.removeEventListener("deviceorientation", this.orientEvent, true);
  window.removeEventListener("devicemotion", this.motionEvent, true);

Sound Module


APIs: WebRTC(getUserMedia), WebAudio

Permissions: audio-capture

Sound: Code

  navigator.getUserMedia({ audio: true },
    function(aLocalMediaStream) { = aLocalMediaStream;
      gModSound.mAudio.context = new window.AudioContext();
      gModSound.mAudio.input =
      gModSound.mAudio.analyzer = gModSound.mAudio.context.createAnalyser();
    function(err) { ... }

  // in window.requestAnimationFrame():
  var data = new Uint8Array(gModSound.mAudio.frequencySlices);
  // ... do something with data ...;

Environment Module

Light, Proximity; Flashlight

APIs: devicelight, deviceproximity events; Camera API

Permissions: ---; camera (for Flash)

Environment: Code

  window.addEventListener("devicelight", this.lightEvent, true);
  window.addEventListener("deviceproximity", this.proxEvent, true);

  lightEvent: function(lightData) {
    lightData.value (in lux)
  proxEvent: function(proxData) {
    proxData.min <= .value <= .max (in cm)

  window.removeEventListener("devicelight", this.lightEvent, true);
  window.removeEventListener("deviceproximity", this.proxEvent, true);

  // flash/torch code works via navigator.mozCameras.getCamera
  // flaky and subject to change, please consult code on github

Device Module


APIs: Battery Status API

Permissions: ---

Device: Code

  0 <= navigator.battery.level <= 1

  .charging (true/false)

  .chargingTime (in s; 0 or Infinity: unknown)

  .dischargingTime (in s; 0 or Infinity: unknown)


Data & Mister Tricorder