Barometer, compass, NFC: ten things your phone already senses
August 25, 2026
* Most of these need no permission prompt. Location and health data are the exceptions.
What's in there
| Sensor | What it knows |
|---|---|
| Barometer | Altitude. Which floor, how far up a trail |
| Gyroscope and accelerometer | Tilt and motion. Shaken, walking, riding in a car |
| Magnetometer | Which way the device is facing |
| Ambient light | Whether it's bright or dark right now |
| NFC | What a tag says when you hold the phone to it |
| Bluetooth proximity | Whether another device is nearby |
| Step count and health | How far someone walked today |
| Front and rear cameras | Both directions at once |
| Haptics | Telling someone without sound |
| Widgets and lock screen | A surface that works without opening the app |
Barometer
Measures altitude. GPS reports altitude too, but the margin of error is wide. A barometer is sensitive enough to tell floors apart.
- Good for: which floor of a building, hiking elevation, a sudden change in weather
- Blocker: readings drift with the day's air pressure. A change in altitude is accurate; the absolute number needs calibrating
Gyroscope and accelerometer
Read tilt and shake. Most phones report hundreds of samples a second.
- Good for: tilt controls, shake to trigger, gait analysis, detecting whether someone is in a moving vehicle
- Cost: free, and no permission needed
Magnetometer
Reports the direction the device faces.
- Good for: orienting a map, "face north" instructions, star charts
- Blocker: magnets and metal throw it off. That figure-eight calibration prompt exists for this reason
Ambient light
Reads how bright the surroundings are. It's the sensor behind automatic screen brightness.
- Good for: apps that change appearance or sound in the dark, features that only open at night
NFC
Reads a tag when the phone touches it. Tags cost a few cents each.
- Good for: linking merchandise to an app with a sticker, access logs, events
- Blocker: iOS allows reading but restricts writing and background scanning
Bluetooth proximity
Detects nearby devices. No server required.
- Good for: pairing with the person next to you, counting who is in a room, exchanging data where there is no internet
- Blocker: Android asks for a separate nearby-devices permission
Step count and health
Reads the step count the phone is already keeping.
- Good for: things that grow or unlock as someone walks
- Blocker: health data has its own permission, and app stores ask you to justify the use
Front and rear cameras
On some devices both can run at once.
- Good for: capturing the viewer and the view together
- Blocker: simultaneous capture is supported on a limited set of devices
Haptics
Strength and duration combine into patterns. Recent hardware manages short, precise taps.
- Good for: silent alerts, games played by touch, guidance for people who can't see the screen
- Blocker: motors differ by device, so the same values feel different
Widgets and lock screen
A surface visible without opening the app.
- Good for: information checked once a day
- Blocker: the operating system decides the refresh interval. Real-time updates aren't available
What's been verified
Capability was checked for all of these. None had been run directly as of this writing.