Accelerometer, gyroscope, magnetometer, microphone, camera, GPS, barometer, LiDAR: a modern smartphone contains up to twenty physical sensors, from which your phone derives more than fifty different measurement instruments. This guide explains, sensor by sensor, how they work, what they really measure, how accurate they are, and how to turn them into scientific instruments for the classroom or at home.
In short: smartphone sensors are industrial-grade components (MEMS technology and microelectronics) capable of serious scientific measurements. The accelerometer measures g to better than 1%, the microphone samples at 44,100 Hz, and the magnetometer detects tenths of a microtesla. Each physical sensor powers several software instruments: the accelerometer also gives you an inclinometer and a pedometer, while the camera gives you a colorimeter, video motion analysis, and a heart rate monitor. Their limits (temperature, electricity, pH) can be overcome with external Bluetooth sensors.
🔬 Try every sensor in two minutes
The free FizziQ app (iOS, Android) turns each sensor described here into a ready-to-use measurement instrument, with more than 120 classroom-tested activities.
In this guide
- One sensor, several instruments: how to read your phone
- The sensor and measurement table
- MEMS and microelectronics: the technology
- The accelerometer · The gyroscope · The magnetometer
- The microphone · The speaker (the reverse sensor)
- The camera · The ambient light sensor
- The GPS · The barometer
- Everyday sensors: LiDAR, touchscreen, proximity, fingerprint
- Raw data, processed data: what your phone hides from you
- What internal sensors cannot measure
- FAQ
One sensor, several instruments: how to read your phone
Two notions are often confused. The sensor is the physical component: a chip a few millimeters wide that converts a phenomenon (force, sound pressure, light, magnetic field) into an electrical signal. The instrument is the software layer that turns this signal into a usable measurement. The same magnetometer gives you a teslameter, a compass, and a metal detector; the same accelerometer gives you a three-axis accelerometer, an inclinometer, a pedometer, and a seismograph.
This software multiplication explains how, with about twenty physical sensors, an app like FizziQ offers more than 50 measurement instruments. Understanding the chain from sensor to signal to instrument to physical quantity is itself a curriculum objective in most physics programs.
The sensor and measurement table
| Physical sensor | Derived instruments | Measured quantities | Unit | Typical accuracy | Rate |
|---|---|---|---|---|---|
| Accelerometer | 3-axis accelerometer, inclinometer, pedometer | linear and absolute acceleration, angles, steps | m/s², °, steps | < 0.01 m/s²; 0.1°; ~1 step in 100 | ≥ 100 Hz |
| Gyroscope | 3-axis gyrometer | angular velocity, rotation | rad/s, rpm | ~0.01 rad/s | ≥ 100 Hz |
| Magnetometer | teslameter, compass, theodolite (azimuth) | magnetic field, orientation | µT, ° | < 0.2 µT; 0.1° (compass) | ≥ 50 Hz |
| Microphone | sound level meter, frequency meter, oscilloscope view, spectrum, spectrogram, acoustic stopwatch | sound level, frequencies, durations | dB, Hz, s | frequency to the Hz; durations to the ms | 44,100 Hz sampling |
| Camera | video motion analysis, chronophotography, colorimeter, luminance meter, heart rate monitor | position, speed, RGB color, absorbance, luminance, pulse | m, m/s, %, bpm | time resolution: 4 ms at 240 fps | 30 to 240 fps |
| Ambient light sensor | lux meter | illuminance | lux | model dependent | ~10 Hz |
| GPS (GNSS) | position, altimeter, speedometer, accuracy readout | latitude/longitude, altitude, speed | °, m, m/s | ~10 m (position); < 1 m/s (speed) | 1 Hz |
| Barometer | barometer, barometric altimeter | atmospheric pressure | hPa | detects ~1 m of elevation change | ~10 Hz |
| External sensors (Bluetooth) | temperature, pH, CO₂, voltage, particulates, and more | sensor dependent | °C, pH, ppm | sensor dependent | sensor dependent |
Orders of magnitude observed on recent smartphones; exact values vary between models, and that variability is itself an excellent lab topic on measurement uncertainty.
MEMS and microelectronics: the technology behind the sensors
Smartphone sensors belong to two families. MEMS (Micro-Electro-Mechanical Systems) contain a genuine moving mechanical microstructure etched in silicon at the micron scale: a mass suspended on springs for the accelerometer, a vibrating mass exploiting the Coriolis force for the gyroscope, a deformable membrane for the barometer and the microphone. The second family is microelectronics with no moving parts: a matrix of CMOS photodiodes for the camera, the Hall effect for the magnetometer, a radio frequency chip for the GPS.
These components are not toys. The same technologies trigger airbags, stabilize drones, and fly in aircraft. Produced by the billions, their price has collapsed: it is the smartphone’s economy of scale, as much as the technology itself, that puts a laboratory in every pocket.
The accelerometer: the king of mechanics
How it works. A microscopic mass suspended on silicon springs moves under inertial forces; the resulting change in electrical capacitance is converted into acceleration along the phone’s three axes X, Y, Z. Full explanation: How does my smartphone’s accelerometer work?
What it measures, and the subtlety to master. The phone provides two distinct quantities. Absolute acceleration is the raw sensor output: it includes the reaction to gravity, so a phone lying on a table reads 9.81 m/s². Linear acceleration subtracts g by computation: the same phone reads zero. In free fall the roles reverse: absolute acceleration drops to zero (weightlessness) while linear acceleration reads g. This distinction, rich in discussions about reference frames, is developed in What is the difference between linear and absolute acceleration?
Derived instruments. A 3-axis accelerometer, but also an inclinometer (angle from the vertical or the horizontal, to 0.1°, a plumb line and a spirit level in one) and a pedometer, which recognizes the regular signature of walking in the acceleration signal (pedometer).
Accuracy. Resolution better than 0.01 m/s², rate above 100 Hz: enough to measure g to better than 1%.
In the classroom. Oscillations of a simple pendulum, elevator physics, circular motion in a salad spinner, shocks and bounces, and seven experiments on gravity.
The gyroscope: rotation in real time
How it works. A vibrating mass experiences the Coriolis force when the phone rotates, the same principle as the balance organs of insects. The sensor deduces the angular velocity around the three axes, in rad/s or revolutions per minute.
In the classroom. Period of a turntable, conservation of angular momentum on an office chair, and the star verification of high school mechanics: combining gyroscope and accelerometer in a salad spinner to verify a = ω²r. The gyroscope is the forgotten sensor of textbooks, yet it is one of the most precise chips in the phone.
The magnetometer: making magnetic fields visible
How it works. Most often through the Hall effect: the magnetic field deflects charge carriers in a semiconductor, creating a measurable voltage along three axes. Some models use the magnetoresistive effect instead: the resistance of an iron-nickel alloy changes with the field. Typical sensitivity: better than 0.2 µT, to be compared with the Earth’s magnetic field of about 47 µT in Europe.
Derived instruments. A teslameter, a compass (angle to magnetic north, to 0.1°), and the azimuth of a theodolite for triangulation measurements.
The teaching paradox. Bring a magnet close: the field reading goes wild, yet the compass keeps pointing north. The answer, permanent software recalibration, perfectly illustrates the difference between raw and processed data: Why is a smartphone compass not affected by magnets?
In the classroom. The Earth’s field and its inclination, the 1/d³ law of a dipole (log-log plot), the Oersted effect around a current-carrying wire, magnetic treasure hunts, and detecting metal structures inside a wall.
The microphone: six instruments in one membrane
How it works. Heir to the electret microphone (a permanently polarized capacitor that consumes almost nothing), the smartphone microphone is now itself a MEMS: a miniature membrane vibrates under the pressure variations of the sound wave, and the signal is digitized at 44,100 Hz with 16-bit resolution (an amplitude precision of 0.003%), which by the Nyquist theorem covers the entire audible spectrum.
Derived instruments. This is the most prolific sensor in the phone: the sound level meter measures loudness in decibels (a logarithmic scale: conversation ~60 dB, blender ~90 dB, pain above 140 dB); the oscilloscope view shows the shape of the wave, the answer to the question can you see a sound?; the frequency meter extracts the dominant and fundamental frequencies through a Fourier transform; the spectrum breaks the sound into its harmonics; the spectrogram tracks the spectrum over time; and the acoustic stopwatch, triggered by a sound threshold, measures durations to the millisecond, the key to measuring the speed of sound.
A limit to know. A phone’s sound level meter is not calibrated like a class 1 device: excellent for comparisons and differences, approximate in absolute terms. A critical thinking challenge built on this: does adding two sounds really increase the level by 3 decibels?
The speaker: the reverse sensor
Always forgotten in sensor inventories: the phone is not only a receiver, it is also an emitter. Its synthesizer generates tones with accurately defined digital frequencies, although the acoustic output of the tiny loudspeaker is neither flat nor calibrated. That is enough to create beats between two close tones, study interference between two loudspeakers, produce the source wave of a Doppler experiment, or investigate the frequency response of a loudspeaker or a resonant system: six experiments with the tone generator. Paired with the microphone of a second phone, it forms a complete emission and reception chain: an acoustics bench made of two devices.
The camera: the richest sensor of all
How it works. A matrix of CMOS photodiodes topped with a Bayer filter, a grid of red (~640 nm), green (~550 nm), and blue (~460 nm) microfilters that reproduces the trichromatic logic of our retina, first described by Thomas Young. Slow motion modes reach 240 frames per second, a time resolution of 4 ms.
Three families of instruments. Kinematics: through video motion analysis (frame-by-frame tracking gives position, velocity, acceleration, and energy) or through chronophotography, which makes motion visible before making it computable. See also the free video library for motion analysis. Colorimetry: RGB intensities, hue, and absorbance, enough to run a Beer-Lambert law titration. Beware of automatic exposure adjustments: lock them before comparing colors. Physiology: finger on the lens, flashlight on, the camera becomes a heart rate monitor through photoplethysmography, a principle demonstrated as early as 1937 by Hertzman and Spealman, and green light works best for it.
The ambient light sensor: a pocket lux meter
A photodiode on the front face measures illuminance in lux through the photoelectric effect: full moon ~1 lux, a classroom ~400 lux, direct sunlight above 30,000 lux. Not to be confused with luminance, computed by the camera, which characterizes what a surface emits or reflects. The distinction is explained in Brightness or luminance? A classic experiment: verify the 1/d² decrease of illuminance with distance.
The GPS: position, speed, and a touch of relativity
The GNSS receiver (GPS, Galileo, GLONASS) triangulates signals from at least four satellites: position to ~10 m, altitude, speed to better than 1 m/s, updated every second. A dedicated accuracy readout displays the error margin in real time, a lesson in metrology by itself. The signal does not pass well through walls or foliage: this is an outdoor sensor. In the classroom: speed of a runner or cyclist, mapping of geolocated measurements (noise, magnetic field), and a natural gateway to relativity, since satellite clocks must be corrected for relativistic effects for your position to be right.
The barometer: one meter of elevation
The MEMS barometer (present on part of the models only, including all recent iPhones) measures atmospheric pressure through the deformation of a membrane, with enough sensitivity to detect one meter of elevation change: measuring the height of a building by taking the stairs, barometric altimetry, and weather tracking.
Everyday sensors: the hidden physics of your phone
About twenty sensors actually live in a smartphone, and even those that are not used for scientific measurement illustrate beautiful physical principles, all worth a classroom discussion.
The LiDAR (on recent high-end models) emits laser pulses and measures their time of flight to map space in 3D, the rangefinder principle, used from archaeology to facial recognition. The proximity sensor pairs an infrared emitter and receiver: if your ear comes within 5 cm, the reflected light is detected and the screen turns off. The capacitive touchscreen is a sensor in its own right: your finger locally modifies the electric field of a conductive layer, so every tap is a capacitance measurement. The fingerprint reader exists in three technologies (optical, capacitive, ultrasonic, the safest). The internal thermometers monitor the battery and the processor, not the ambient air, and the hygrometer made a brief appearance (Galaxy S4 and S5, capacitive measurement of water vapor) before being dropped: two illustrations of the fact that an embedded sensor measures the phone first and the world rarely. For environmental quantities, the external sensor remains the right answer.
Down to the buttons, binary sensors tested 100,000 presses in the factory: the humblest sensor may be the most indispensable.
Raw data, processed data: what your phone hides from you
The smartphone almost never delivers the bare physical signal. The magnetometer is permanently recalibrated (the secret of the magnet-proof compass), linear acceleration is a quantity computed by sensor fusion (the system permanently combines accelerometer, gyroscope, and magnetometer into a virtual orientation sensor), the camera automatically adjusts exposure and white balance, the microphone sometimes applies noise reduction, and the software sound level meter works in relative terms for lack of absolute calibration. Understanding what separates the sensor’s signal from the displayed value (calibration, fusion, filtering, measurement noise) is one of the most valuable lessons these instruments offer: a measurement is never a truth, it is a processed signal.
What internal sensors cannot measure
An honest inventory has empty columns. Temperature of the air or a liquid (internal probes watch the phone, not the world), voltage and current, pH and solution chemistry beyond indirect colorimetry, radioactivity (despite what some apps claim), and any certified metrological precision measurement. For these quantities, the answer is an external Bluetooth sensor, which is exactly the role of FizziQ Connect (temperature, pH, CO₂, voltage, particulates), or a microcontroller (micro:bit, Arduino, ESP32) built by the students themselves.
In short
Twenty physical sensors, fifty software instruments, most of the secondary school curriculum covered: the smartphone is a multimeter for the real world. Its deepest lesson goes beyond any single measurement: between the phenomenon and the displayed number, there is a sensor, a conversion, a processing step, and an uncertainty. That is exactly what a scientist must learn to question.
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All these instruments are gathered in FizziQ (free, ad-free, works offline), and you can explore the library of 120+ activities to begin.
FAQ
How many sensors are there in a smartphone? Up to about twenty. Virtually all models include an accelerometer, gyroscope, magnetometer, microphone, camera, ambient light sensor, proximity sensor, touchscreen, and GPS; the barometer, LiDAR, and fingerprint reader are only found on some devices.
What is the difference between a sensor and a measurement instrument? The sensor is the physical component that converts a phenomenon into an electrical signal; the instrument is the software that turns this signal into a measurement. A single accelerometer thus powers a 3-axis accelerometer, an inclinometer, and a pedometer.
Are smartphone sensors accurate? Yes, for most school uses and well beyond: acceleration to 0.01 m/s², sound frequencies to the hertz, magnetic field to 0.2 µT. Academic publications have validated these sensors for university-level lab work.
Why does the accelerometer read 9.81 m/s² at rest? Because it measures absolute acceleration, which includes the reaction to gravity: its internal mass is held by its springs against the pull of the Earth. Linear acceleration, computed by the phone, subtracts this component and reads zero at rest.
Can a smartphone measure temperature? No: internal probes measure the battery and processor temperature, not the air. You need an external Bluetooth sensor, for example through FizziQ Connect.
How does the phone know where north is despite its own magnets? The system permanently recalibrates the magnetometer to subtract the fixed fields of the phone and its immediate surroundings; only the Earth’s component is used by the compass.
Why do my measurements differ from another phone’s? Each model carries sensors from different manufacturers and generations, with their own calibrations. Comparing measurements across devices is an excellent lab exercise on dispersion and uncertainty.
Do sensors need an internet connection? No, they all work in airplane mode. Only the GPS needs to receive satellites, but no mobile network.
Further reading: this article is part of our complete guide to measuring and analyzing sound with a smartphone or computer.