All smartphones have sensors, even the cheapest ones. It’s part of what makes them smart. They use the sensors to “sense” what’s going on around them and respond accordingly.
The number of sensors found on a smartphone depends mostly on the manufacturer’s design and the price range of the phone. There are approximately close to twenty different types of sensors you can find on a phone. Some of them are very common, while others you might not have even thought of as a sensor at all.
High-end smartphones are fitted with as many sensors as the manufacturer deems necessary for the ultimate mobile experience. Cheaper smartphones, on the other hand, usually have very basic sensors to keep the costs of production low.
But what exactly are these sensors, and what purpose do they serve? Find out below.
Types of sensors found on mobile phones
The following are sensors commonly found in today’s smartphones. They are known as base sensors because they have a physical sensor they represent, after which they are named. Base sensors relay information from one physical sensor only.
Biometric sensors
Biometric sensors often relate to security. The term ‘biometrics’ refers to physical characteristics that can be used to identify a person. Examples of biometrics include your DNA or fingerprints.
Because nobody shares the same biometrics, these sensors are the highest form of security you can have against unauthorized access to your phone.
A biometric sensor uses your physical characteristics to identify you and unlock your phone. In smartphones, the preferred biometrics are your fingerprint, your eyes, and your face.
Fingerprint scanner
Perhaps the most well-known of all sensors on a smartphone, the fingerprint sensor works as a security measure to verify the identity of a registered user of the smartphone using their unique fingerprint. This biometric identity verification method is used to unlock the smartphone and execute online money transactions.
Fingerprint sensors are not common on cheap, entry-level smartphones. Some mid-range smartphones come with pretty decent fingerprint scanners that work really well. But the best and fastest-responding fingerprint sensors are found in high-end smartphones. That includes under-display fingerprint scanners.
Iris scanner
If you’re a fan of spy movies, you may have seen scenes where a laser scans an agent’s eye before unlocking the doors to a top-secret location. That’s essentially the same thing a phone with an iris scanner does to unlock your phone. It shoots a harmless infrared light into your eye to scan the pattern of your iris.
Just like fingerprints, no two people’s irises are the same. Even both your irises don’t match. So, remember to use the correct eye to unlock your phone, or capture the iris pattern of both your eyes when setting up the scanner.
Facial recognition
Facial recognition software on a smartphone looks at your face and analyzes its construction. It then compares the face to its database of recognized faces. Once it finds a match, it will unlock the phone. Facial recognition usually works in conjunction with the front-facing camera but sometimes it has its own dedicated sensor.
In my opinion, face recognition is the least secure of the biometric sensors. It can be fooled and has been said to have difficulty recognizing dark skin faces.
Ambient light sensor
Most smartphones, regardless of the price range, come equipped with an ambient light sensor. This sensor analyses the lighting conditions of the environment that you’re in and adjusts the brightness of your phone’s screen to give you a good viewing experience.
Another use for the ambient light sensor is for auto-white balance (AWB) when taking photos with your smartphone. Auto-white balance analyses the lighting in the scene and helps the camera adjust its colours to reproduce the scene as best as possible. Otherwise, you have to do it yourself manually.
Proximity sensor
The proximity sensor works both to save battery power and to avoid unintentional input while you’re on a call. What it does is it senses the presence of nearby objects without any contact.
A smartphone with a proximity sensor can, for example, turn the phone screen on as you reach for the phone, and have it ready for use. When you put the phone down and move away from it, the screen will switch off.
And while you’re on a call, the proximity sensor will detect that the phone is close to your ear and have the screen switched off. This will help you avoid accidentally ending the call with your ear or cheek or any other input that may interfere with the call.
Once you remove the phone from your ear, the screen will switch back on, enabling you to interact with your smartphone as you wish.
Accelerometer
An accelerometer senses a smartphone’s movement. It analyses the acceleration, vibration, and tilt of the phone in order to determine its exact position, orientation, and movement along the X, Y, and Z axes.
That means the accelerometer allows the phone to detect if it’s being held horizontally or vertically, and then rotate the display. It is also responsible for counting your daily steps and recognizing motion gestures of the phone.
Examples of the accelerometer at work include shaking the phone to change a song, flipping the phone face down to mute a ringtone, tilting the phone to steer while playing a mobile game, changing between portrait and landscape mode when taking photos or recording videos, and so on.
Pretty much every smartphone has an accelerometer. What the phone can do with the data from this sensor differs from device to device. For example, two smartphones may both have an accelerometer, but maybe only one of them has the “flip to mute” function.
Gyroscope
The gyroscope, or simply gyro, is similar to the accelerometer, but more advanced. It also provides orientation details and direction, but with even better precision. While the accelerometer works well to detect movement and rotation on a certain axis (i.e., rotating the phone horizontally to switch to landscape mode), a gyroscope works with the accelerometer to calculate the exact amount of movement in degrees.
So, the gyroscope not only senses right/left, up/down, and forwards/backwards motions, it also detects the roll, yaw, and pitch motions. These are rotations on the X, Y, and Z axes that the accelerometer cannot sense and measure.
This is what enables it to be so precise in detecting motion in a smartphone because it can tell in which direction the phone is turned and by precisely how much.
This particular sensor is useful in applications such as motion-sensitive games such as car-racing games, VR and augmented-reality applications, as well as taking panoramic shots with your mobile camera.
Magnetometer
A magnetometer is a device that’s used to measure magnetic forces, particularly the magnetism of the earth. It measures the strength and direction of the magnetic field around the magnetometer.
In smartphones, a magnetometer works along with other sensors that are responsible for determining where the phone is in physical space (e.g., accelerometer, GPS, etc.) when you’re using navigation software such as Google Maps and Apple Maps. By measuring the magnetic field around it, it can figure out which way is north and work out which way the map should face.
What’s more, with the correct app, the magnetometer can turn your smartphone into a hand-held metal detector.
Hall sensor
While on the topic of sensing magnetic fields, some smartphones come with a hall sensor which is basically a device that measures the magnitude of a magnetic field.
A simple example of a hall sensor at work in a smartphone can be seen when using a smartphone case with a magnetic cover. When the cover closes on the phone, the hall sensor detects the proximity of a magnet and switches the screen off. When the cover is lifted, the hall sensor will sense the absence of the lid and the screen will switch on again.
Altimeter
An altimeter is an instrument used to measure the height above sea level. On smartphones, an altimeter is perfect for people who enjoy high-altitude outdoor activities such as hiking, mountain biking, skiing, etc.
Barometer
A barometer is used to measure the surrounding atmospheric pressure. In simple terms, it can tell you how heavy the air around you is. Barometers are often consulted when looking at weather trends. If the reading of the air pressure is high, it indicates good weather. Poor weather is indicated by low-pressure readings on the barometer.
Similar to an altimeter, a barometer can determine your vertical location. Whenever you change elevation, the barometer reads the difference in air pressure to get a sense of how high you are. However, a barometer cannot tell you exactly how high you are above sea level without a reference air pressure reading.
Depth Sensor
Source: ubergizmo.com
Often listed as one of the rear (or sometimes front-facing) cameras and also referred to as a time-of-flight camera, a depth sensor is used to create a three-dimensional map, or depth map, of the environment. It does so by shooting out a laser and calculating the time it takes to bounce off nearby objects and reflect back to the sensor.
Obviously, the laser will reflect off objects in the foreground quicker than those in the background. The data is combined and the depth is calculated. This information can be used when taking photos to blur the background, or in augmented reality applications.
Starting with the iPhone 12 Pro, Apple introduced a LiDAR scanner to its list of sensors. LiDAR, or Light Detection And Ranging, is similar to the ToF (time-of-flight) sensor but instead of firing one laser, it fires multiple lasers for a more accurate 3D map of the environment.
ALSO READ: What Is A ToF Camera? And How Does It Work?
Soli
Developed by Google and introduced to smartphones with the Pixel 4, Soli is a motion sensor that can read and understand human movements, big or small, from all angles. According to Google, Soli can even detect objects and motions through various objects. It’s not a camera, so it doesn’t need to “see” any movement to detect it.
Simply put, Soli works by emitting electromagnetic waves in a broad beam and then detecting the objects that reflect some of the energy back to the radar antenna. The data that’s collected and analyzed includes information about the size, shape, and movement of the object, amongst other things. It can even sense small and complex finger movements that are made within its range.
The Soli chip basically allows you to use your phone without touching it. You can unlock your phone, skip songs, browse through photos, silence your phone, and so much more, all without touching your phone. Check it out in action in the video below.
Sound sensor
Every smartphone comes with a sound sensor that picks up changes in the surrounding airwaves. This “sensor” is commonly known as a microphone. Whenever something makes a sound, the air around it expands and contracts, causing waves similar to the ripples on a body of water.
Microphones detect the sound waves created by the expansion and rarefication of the air and turn this into a sound we can hear through a speaker. Smartphones use tiny MEMS microphones which uses micro-electromechanical systems to pick up sound.
Illustration of a smartphone MEMS microphone
A Smartphone microphone is commonly active during a call or when using an app that requires audio input. However, as a general audio sensor, the microphone can pick up on specific sounds such as voice commands even when no app that requires the microphone is running. An example is Apple’s Siri.
Image sensor
No mobile camera would ever be able to function without an image sensor. In essence, an image sensor is an instrument that captures light and creates an image from it. It’s made up of millions of light-sensitive photosites (aka pixels) collectively known as megapixels.
Therefore, if a camera is said to be 12MP, it basically means the image sensor has twelve million photosites that capture the light that enters the camera. A large mobile camera sensor can accommodate bigger pixels, which is great for taking photos in low-light conditions.
ALSO READ: The Smartphone Camera Sensor- A simple introduction [UPDATED]
Touchscreen
Touchscreen sensors are perhaps the most used sensor on any smartphone. A phone’s screen not only detects when it has been touched, but it also knows where it has been touched. How a touchscreen is able to sense touch input depends on whether it is a resistive or capacitive touchscreen.
ALSO READ: How Does A Smartphone Touchscreen Work
Humidity
Rarely found on many smartphones today, the air humidity sensor does as its name says and measures the amount of humidity in the air. The first popular smartphone to feature a humidity sensor was the Samsung Galaxy S4 back in 2013. Very few phones have followed suit since.
Thermometer
Another not-so-common sensor pioneered in smartphones by Samsung’s Galaxy S4, the thermometer gives you a reading of the ambient temperature of the environment you’re in. Although technically every smartphone comes with a heat sensor to monitor the phone’s internal temperature, not all smartphones have a sensor to tell you how hot or cold it is where you are.
Heart rate sensor
A heart rate sensor measures the heart rate of the person touching the device in beats per minute (BPM) using an optical LED source and an LED light sensor. The light shines through your skin and measures the pulses as blood moves past the light, which is interpreted as heartbeats.
On certain phones, to read your heart rate, you can place your finger on the same sensor with which you would unlock your phone with your fingerprint. In cases like that, the heart rate sensor technically qualifies as a composite sensor.
Composite sensors
Smartphones also have what is known as composite sensors. A composite sensor generates data by processing data from one or more other physical sensors because they do not have their own physical sensor from which they can draw data.
An example of a composite sensor is the step calculator that tells you how far you have walked and how many steps you have taken. There is no physical sensor that calculates how many steps you take. Rather, this information is gathered from the accelerometer and possibly other sensors for added accuracy.
Special mention: Radiation sensor
This is one sensor you will hardly find on any popular phone on the market. In fact, the only phone I have ever heard of that has a radiation sensor is the Pantone 5 107SH by SoftBank, which was only released in Japan after the Fukushima nuclear disaster of 2011.
A button on the front of the phone triggers a dedicated radiation reader app that measures the amount of radiation in the area and gives you a reading within ten seconds, according to SoftBank.
Let’s hope to never live in a world where this sensor will have to be on every phone on the market.
Conclusion
As I already stated in the beginning, all smartphones have sensors because it’s part of what makes them smart as they are. However, the more sensors a phone has, the pricier it becomes. Therefore, cheap smartphones have minimal sensors and their quality tends to be not that great.
But even high-end smartphones don’t have all the sensors on this list. Some may have fallen out of favour to make room for other technology. However, knowing smartphone manufacturers and how they like to bulk up the specs of their phones, it wouldn’t be surprising to find a phone that has all these and more in the future.
