How Do Smartphone Sensors Work? A Short Guide

We grew so accustomed to smartphones being an integral part of our daily lives that we often forget how impressive our little pocket buddies are. Smartphones are practically tiny computers with hardware that can go toe-to-toe with slightly older desktop PCs and many modern laptops.

A significant portion of smartphones’ capabilities and flexibility stems from mobile sensors - a combination of cellphone hardware and software that detects things like the device’s location, environmental conditions, and user identity. 

But, how do smartphone sensors work, and which types of sensors can you find on modern smartphones? Read on to find out.

Smartphone Sensor Types

You’d be surprised by just how much we rely on sensors to perform daily tasks on our mobile phones. While most of us are aware of the more apparent sensors like the ones used in GPS or the fingerprint sensor, newer smartphones can have more than ten different detectors embedded within them.

Smartphone sensors can be divided into several categories:

Motion sensors - the purpose of these is to detect smartphone movement, such as shaking, tilting, or swinging. 

Environmental sensors - these serve to assess various environmental factors such as humidity, temperature, or pressure.

Positional/location sensors - with these types of sensors, your smartphone can tell you your current location on the map.

Biometric sensors - a smartphone biometric sensor is usually used as a security feature to restrict access to unauthorized users by scanning fingerprints or facial features.

Proximity sensors - as their name suggests, proximity sensors help your phone detect how close certain objects are to a specific part of your phone.

It’s important to note that not all mobile phone sensors can fit into one of these categories. For example, the heartbeat sensor isn’t a part of any of these sensor groups. Furthermore, some sensors might belong to multiple categories and often work in conjunction with others to allow the phone to perform certain functions. 

Of course, it’s not easy making a definitive smartphone sensors list, as there are tons of different configurations on the market. For example, the high-end LiDAR sensor is found mainly in top-tier Apple devices. With that in mind, we’ve covered only the most common sensor types here. 

Phone Sensors: An Overview

After answering the question “How do smartphone sensors work?” let’s talk a bit about the different types of sensors you can find in most of today’s smartphones.

Accelerometer

Accelerometers are sensors tasked with detecting movement and orientation across all three axes by registering things like tilt, vibration, and acceleration. If you’ve ever wondered how various navigation apps know whether you’re moving on foot or in a vehicle, this is how. 

Furthermore, health & fitness apps, just like smartwatches and fitness bands, rely on the accelerometer to measure the number of steps you take daily.

The way an accelerometer in smartphones functions is through the use of tiny crystal structures (usually quartz or tourmaline) that react to acceleration. The other sensors found in accelerometers pick up voltage readings emanating from these crystals to detect and measure movement. Impressive, isn’t it?

Besides detecting the speed of movement, the accelerometer’s ability to determine the direction you’re facing is also invaluable. This is especially true when it comes to the increasingly popular Augmented Reality apps and gadgets, which require information on where the user is facing at all times to function correctly.

Gyroscope 

A gyroscope performs a similar function as an accelerometer, as both serve to help your device get a sense of your phone’s orientation. However, a gyroscope is more precise and can detect the rotation of your phone - something accelerometers cannot do.

When comparing the accelerometer vs. gyroscope, the latter is used to detect subtler movements like tilting your screen to one side. While precise for faster movements and driving, accelerometers can’t really pick up these tiny movements accurately (or at all, in some cases).

The gyroscope consists of a small vibrating plate positioned on a chip. That plate gets moved by Coriolis forces when your phone’s orientation changes, with the chip registering those movements and detecting the device’s precise orientation.

Accelerometers and gyroscopes are no rivals, though. In fact, they’re usually used in conjunction to get the most accurate orientational readings. There are plenty of uses for a  gyro sensor in a phone. One of its most common applications is in mobile games, where the player can steer a car by tilting the phone left and right. Additionally, many phone-related commands such as turning the flashlight on or making a call can be tied to specific phone movements that the gyroscope can detect.

Phone Magnetometer 

Practically every smartphone comes with a built-in magnetometer, i.e., a compass. The magnetometer detects and measures magnetic fields, which lets the sensor determine your location in relation to the North Pole.

Along with the accelerometer and gyroscope, the magnetometer is also to thank for the precise location readings our phones provide us with. By using these three sensors, complete orientation of the phone across the yaw, pitch, and roll axes can be achieved.

In practically all navigation apps such as Google Maps, the magnetometer helps recenter your map and lets the app provide proper navigation guidance. Of course, the magnetometer is also used for compass apps as well.

Lastly, a magnetometer in phones can pick up magnetic metals, which is how metal detecting apps on your smartphone operate.

GPS

GPS (Global Positioning System) has thoroughly changed the world, leading to what amounts to a hyperspace jump in our navigational abilities - from driving cars and airplanes to coordinating military actions.

The GPS represents the final piece in the smartphone location tracking puzzle. The system narrows down your position on Earth by communicating with space satellites. Communication with satellites does not rely on an internet connection, meaning you can use the mobile GPS sensor even when you don’t have access to the internet or your mobile network. However, the quality of the map you’ll have access to will suffer as a result.

One more thing to note is that GPS sensors don’t rely on satellite information alone, nor do they always act independently from other location sensors in your phone. 

Proximity Sensor

The proximity sensor utilizes an IR LED and light detector to determine whether any external objects are close to the phone. 

The main use of this sensor is to shut down your display and touchscreen during phone calls to prevent you from accidentally pressing something with your ear or cheek. Besides preventing accidental hangups, the cell phone proximity sensor also helps conserve battery while on a call since the screen is turned off when close to your face. 

Ambient Light Sensor

As its name suggests, the ambient light sensor’s purpose is to detect the light levels in your surroundings. This sensor is mainly used by the auto-brightness feature, which fine-tunes your phone’s brightness options based on how much light is around.

The sensor utilizes a photodetector to measure luminance. Thanks to the ALS, you can avoid having the screen too bright or too dark in certain environments, which helps reduce eye strain.

Smartphone Biometric Sensors

Biometric sensors usually encompass fingerprint and face recognition systems that help authenticate the phone’s owner and let you unlock your phone by using your fingerprint or a face scan. When they first launched, they were considered a pretty revolutionary step in phone security, as they protect your phone significantly better than PIN codes or unlock patterns.

When it comes to fingerprint scanners, these can scan with light, sound, or through electronic capacitors. Both fingerprint and facial recognition scanners are combined with software and advanced algorithms to make recognition more accurate and security tighter.

Touchscreen Sensor

The touchscreens found on smartphones are, naturally, reliant on sensors too. This mobile sensor works by sending electrical currents through the screen whenever it is touched. These currents pass through three layers - the glass lens, the electrical grid, and the LCD.

Initially, resistive screen technology was the name of the game. However, when Apple pushed out the capacitive touchscreen, this became the technology predominantly used by smartphone manufacturers.

Heart Rate Sensor

Smartphone heart rate sensors are impressive tech, even compared to other sensors we’ve talked about so far. These sensors use an optical LED light and a LED light sensor. This light shines on your skin, with the sensor picking up the amount of light reflecting back. 

As your blood pulses, these pulses under your skin pass the sensor’s light. Based on these readings (changes in the color and opacity of the blood as it gets pumped through the body), your phone can divulge your current heart rate. This is, of course, used by many health apps, and the technology can be used to approximate the number of calories burned as well.

Environmental Sensors

Lastly, we have environmental sensors. These are used to assess various environmental factors. The ones most commonly found in smartphones are the thermometer (measures temperature), the barometer (measures pressure), and the air humidity sensor.

There’s also a phone that shipped with a built-in Geiger sensor called the Sharp Pantone 5. This phone was released exclusively in Japan and can measure radiation levels around you with 20% accuracy. If you’re planning a trip down to Pripyat, make sure to get one of those.