doodlesensor

Fact sheet · updated

A PLAIN-ENGLISH GUIDE

The sensors
in your pocket.

Your phone is quietly measuring the world around it.

Find the sensor behind it
An unbranded phone on a pale oak table with its back cover and circuit board laid beside it, next to a brass compass, a spirit level and a folded map
AI-generated image, not a photograph of a real person or place.

SENSEtilt · turn · find

It feels gravity, rotation and Earth’s magnetic field. It reads air pressure and light, notices your ear, and listens for satellites about 20,200 km overhead. Here is what each sensor does, and how far to trust it.

Plain English, with the sources linked.

At a glance

4.9 m radius

Typical phone accuracy, open sky

GPS-enabled smartphones are typically accurate to within a 4.9 metre (16 ft) radius under open sky. Near buildings, bridges and trees, that accuracy gets worse.

LOCATION · GPS.GOV

1 hPa per 10 m

Pressure change near the ground

Air pressure drops by about 1 hectopascal for each 10 metres of height near the surface. That is why a barometer can notice a climb of a few floors.

HEIGHT · MET OFFICE

TWO NUMBERS WORTH KNOWING

Where you are,
how high you are.

One comes from satellites,
the other from the air around you.

Both are typical figures, not guarantees. Your surroundings, the weather and the quality of the receiver all change what a phone actually reports.

A QUICK SENSOR CHECK

Which sensor
is doing that?

Pick something your phone does every day and see which sensor is behind it.

Not every phone has every sensor. Barometers in particular are missing from some models, and many features combine readings from several sensors at once.

Sensor check

Choose an everyday feature
Screen turns sidewaysAccelerometer

It measures acceleration along three axes, including the pull of gravity, so the phone can tell which way is down as you turn it.

Panorama or game steeringGyroscope

It measures how fast the phone rotates around each axis. Adding that rate up over time gives the angle it has turned.

Map arrow faces your wayMagnetometer

It senses Earth’s magnetic field, which is faint: roughly 25,000 to 65,000 nanotesla at the surface.

Which floor you are onBarometer

It reads air pressure. Near the ground, pressure falls by about 1 hPa for every 10 metres you climb.

Screen goes dark at your earProximity sensor

It detects an object close to the screen and is typically used to tell when the phone is held up to your ear during a call.

The blue dot on the mapSatellite receiver

It times signals from navigation satellites. Under open sky a phone is typically accurate to within about 4.9 metres.

Sources are listed at the foot of the page.

THE SHORT ANSWER

Three jobs, many sensors.

Phone sensors fall into three broad groups:
motion, position and environment.

MOTION

Accelerometer and gyroscope

One feels acceleration and gravity, the other rotation. Together they know how the phone is held and moved.

Try the sensor check

POSITION

Compass and satellites

The magnetometer finds magnetic north; the satellite receiver works out where you are, best under open sky.

How accurate?

ENVIRONMENT

Pressure, light and proximity

A barometer reads air pressure, a light sensor sets screen brightness, and a proximity sensor notices your ear.

See the numbers
Two hands tilting an unbranded phone above a stone table, beside a small brass gyroscope
AI-generated image, not a photograph of a real person or place.

GET BETTER READINGS

Four habits
for steadier sensors.

  1. Give it a view of the sky

    If the blue dot wanders, step away from tall buildings and out from under bridges or trees before trusting the position.

  2. Keep magnets away from the compass

    The field the compass reads is faint, so magnetic mounts, clasps and nearby metal can pull the arrow off course.

  3. Know which north you are using

    Magnetic north and true north differ by the local declination. Check which one your map or compass app is showing.

  4. Treat barometer height as relative

    Weather moves air pressure too, so a barometric height is best for comparing floors or a climb, not for an exact altitude.

SENSOR FACTS

Five things worth
knowing.

  1. The satellites are a long way up

    GPS satellites fly about 20,200 km above Earth and circle it twice a day. The United States commits to at least 24 working satellites, and has flown 31 for well over a decade.

  2. Sky blockage costs accuracy

    What your phone receives depends on satellite geometry, signal blockage, the atmosphere and the receiver itself. Buildings, bridges and trees all make the fix worse.

  3. The compass reads a faint field

    Earth’s magnetic field at the surface is only about 25,000 to 65,000 nanotesla. Near the magnetic poles, NOAA marks zones where compasses become unreliable.

  4. Magnetic north is not true north

    The angle between them is called magnetic declination, and it changes from place to place. A map app has to correct for it to point you the right way.

  5. The gyroscope is a tiny vibrating beam

    In phones, microscopic beams are kept vibrating. When the phone turns, the Coriolis effect nudges them sideways, and that tiny motion reveals how fast it is rotating.

An unbranded phone resting on a weathered fence post beside a brass compass, with open sky and soft green hills behind
AI-generated image, not a photograph of a real person or place.

QUICK QUESTIONS

Sensors, answered.

Short answers to the questions people ask most.

How accurate is the GPS on my phone?

According to GPS.gov, GPS-enabled smartphones are typically accurate to within a 4.9 metre radius under open sky. Accuracy gets worse near buildings, bridges and trees.

How does my phone know which way is down?

The accelerometer measures acceleration along three axes, and its reading includes the force of gravity. That tells the phone how it is tilted, which is how the screen knows when to rotate.

How can a phone tell which floor I am on?

Phones with a barometer measure air pressure in hectopascals. The Met Office notes that near the surface pressure drops by about 1 hPa for each 10 metres of height, so a change of a few tenths of a hectopascal can show a change of floor. Weather also moves pressure, so the reading works best as a short-term comparison.

Why does the compass sometimes point the wrong way?

The magnetometer senses Earth’s magnetic field, which is weak: about 25,000 to 65,000 nanotesla. Nearby magnets and metal can disturb it, and close to the magnetic poles NOAA describes zones where compasses are unreliable.

What do the proximity and light sensors do?

The proximity sensor detects an object close to the screen and is typically used to tell when the phone is held to your ear during a call. The ambient light sensor measures light level in lux and is used to control screen brightness.

Sources

Where the facts come from

  1. GPS accuracy: how accurate is GPS?GPS.gov
  2. The GPS space segment: constellation and orbitsGPS.gov
  3. Geomagnetism frequently asked questionsNOAA National Centers for Environmental Information
  4. How we measure atmospheric pressureMet Office
  5. Coriolis vibrational gyroscopePurdue University, ME 274
  6. Sensors overview: motion, position and environment sensorsAndroid Developers

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