Types of Fingerprint Sensors in Mobile Phones: Complete Guide

Published: 13 Aug 2026

Have you ever wondered why some phones have fingerprint sensors on the side, while others hide them under the display?

Many users think side-mounted, rear-mounted, and in-display scanners are completely different sensor types. However, these terms mainly describe the sensor’s location. The actual technologies used in mobile phones are capacitive, optical, and ultrasonic.

In this guide, you’ll learn about the different types of fingerprint sensors in mobile phones, how each one works, where it is commonly used, and how they differ in speed, accuracy, and convenience.

Table of Content

What Is a Fingerprint Sensor in a Mobile Phone?
How Many Types of Fingerprint Sensors Are Used in Mobile Phones?
Capacitive vs Optical vs Ultrasonic Fingerprint Sensors
Types of Fingerprint Sensors Based on Their Position
Does a Screen Protector Affect the Fingerprint Sensor?
Why Does a Fingerprint Sensor Fail to Recognize a Finger?
How to Improve Fingerprint Recognition
Common Fingerprint Sensor Myths
Conclusion

What Is a Fingerprint Sensor in a Mobile Phone?

A fingerprint sensor is a biometric security component that scans the unique pattern of ridges and valleys on your fingertip.

Fingerprint recognition can be used to:

Unlock the mobile phone
Approve mobile payments
Open protected applications
Confirm purchases
Access saved passwords
Verify identity in banking applications
Protect private files and folders

How Many Types of Fingerprint Sensors Are Used in Mobile Phones?

The three main fingerprint sensor technologies used in mobile phones are:

Capacitive fingerprint sensor
Optical fingerprint sensor
Ultrasonic fingerprint sensor

Each type captures your fingerprint differently.

Types of fingerprint sensors diagram showing capacitive, optical and ultrasonic in-display fingerprint sensors on three phones.

1. Capacitive Fingerprint Sensor

A capacitive fingerprint sensor uses a group of very small electrical components to detect the pattern of your finger. When you place your finger on the sensor, the raised ridges and lower valleys create different electrical signals. The sensor measures these differences and creates a digital representation of your fingerprint.

Capacitive fingerprint sensors became popular in smartphones because they are compact and can provide fast, reliable fingerprint recognition.

Where Are Capacitive Fingerprint Sensors Located?

Capacitive sensors are commonly found:

On the back of the phone
Inside the side power button
Below the display
Inside a physical home button
On the front bezel

A side-mounted fingerprint reader is usually a capacitive sensor built into the phone’s power button. Rear-mounted sensors also commonly use capacitive technology.

Advantages of Capacitive Fingerprint Sensors
They normally unlock the phone quickly. They provide reliable recognition when the finger is clean. They do not need a bright light to scan the finger. They can be placed inside a small button. They work in both bright and dark environments. They are commonly used in affordable and mid-range phones. They usually consume little power.

Disadvantages of Capacitive Fingerprint Sensors
They require direct contact with the sensor. Very dry, wet, dirty or damaged fingers may not scan properly. The physical sensor takes up space on the phone body. A small side-mounted sensor may require more precise finger placement. A thick phone case can make a side sensor harder to reach. Scratches or dirt on the sensor may reduce recognition accuracy.

Is a Capacitive Fingerprint Sensor Good?

A capacitive sensor is a good choice for users who value speed and reliability. It may not look as modern as an in-display scanner, but a well-made capacitive sensor can be faster and easier to use than some low-quality in-display sensors.

2. Optical Fingerprint Sensor

The optical fingerprint scanner works using light to create a picture of your fingertip.

As soon as you press your finger against the fingerprint recognition section, the screen illuminates your finger. A little camera beneath the screen picks up the light bouncing back off the ridges and grooves.

Your phone will compare this picture against the stored fingerprint data template.

According to Samsung Display, optical fingerprint-on-display sensors use light, and ultrasonic sensors use sound.

Where Are Optical Fingerprint Sensors Used?

Optical fingerprint sensors are mainly used under the displays of smartphones.

They are commonly found in:

Budget phones with AMOLED displays
Mid-range Android phones
Some premium Android devices
Phones designed with an edge-to-edge display

When an optical fingerprint sensor is active, you may notice a bright light under your finger. The light helps the sensor capture a clear fingerprint image.

Advantages of Optical Fingerprint Sensors
They enable the placement of the fingerprint reader beneath the screen. They help achieve a neat smartphone design without a fingerprint scanner. They are usually cheaper than the ultrasonic in-display sensors. They are easy for manufacturers to integrate into most OLED smartphones. The sensor area is usually clearly shown on the lock screen. They can provide fast unlocking when properly optimized.

Advantages of Optical Fingerprint Sensors

They enable the placement of the fingerprint reader beneath the screen.
They help achieve a neat smartphone design without a fingerprint scanner.
They are usually cheaper than the ultrasonic in-display sensors.
They are easy for manufacturers to integrate into most OLED smartphones.
The sensor area is usually clearly shown on the lock screen.
They can provide fast unlocking when properly optimized.

Disadvantages of Optical Fingerprint Sensors
They normally capture a two-dimensional image. They need light to read the fingerprint. The bright scanner light may be noticeable in a dark room. Dirt, oil, moisture or very dry skin may affect recognition. Thick or poorly fitted screen protectors can reduce performance. They may require firmer or longer finger contact. Some optical sensors have a relatively small scanning area.

How Can You Identify an Optical Fingerprint Sensor?

Your phone probably has an optical fingerprint sensor when:

The sensor is under the display.
A bright light appears under your finger.
The scanner briefly illuminates part of your fingertip.
The phone uses an OLED or AMOLED display.
The manufacturer describes it as an optical in-display sensor.

Not every in-display fingerprint reader is optical. Some premium phones use ultrasonic technology instead.

3. Ultrasonic Fingerprint Sensor

An ultrasonic fingerprint scanner is designed to use ultrasonic waves of high frequency to recognize fingerprint patterns.

An ultrasonic wave is sent from the scanner towards the finger. The ridges and valleys of your fingerprint reflect these waves differently, allowing the sensor to create a detailed representation of the fingerprint.

According to Qualcomm, its 3D Sonic technology works by using ultrasonic pulses to read the ridges and valleys of the finger, not by photographing.

Where Are Ultrasonic Fingerprint Sensors Used?

Ultrasonic fingerprint sensors are usually placed under the phone’s display.

They are more commonly found in:

Premium smartphones
Selected flagship Android phones
Some Samsung Galaxy devices
Phones using advanced Qualcomm fingerprint technology

Advantages of Ultrasonic Fingerprint Sensors
They do not need a bright light to scan the finger. They can collect detailed fingerprint depth information. They can scan the fingerprint through the phone’s display. They support a clean, button-free phone design. They can include anti-spoofing features. They may work better than optical sensors in some lighting conditions. Newer versions can offer larger scanning areas.

Disadvantages of Ultrasonic Fingerprint Sensors
They are usually more expensive to produce. They are mainly available in higher-priced phones. Some screen protectors may reduce their performance. Incorrect finger placement can cause failed scans. A damaged display or sensor area may affect recognition. Early ultrasonic sensors sometimes had smaller scanning areas.

Is an Ultrasonic Fingerprint Sensor Better?

An ultrasonic fingerprint sensor is generally considered the more advanced under-display option because it uses sound waves rather than relying only on a visible image.

However, the real experience depends on the quality of the sensor, its size, the phone’s software, finger condition, display condition and screen protector.

Capacitive vs Optical vs Ultrasonic Fingerprint Sensors

Each fingerprint technology has its own strengths and limitations. Here’s a quick comparison of capacitive, optical, and ultrasonic sensors

Feature	Capacitive	Optical	Ultrasonic
Scanning method	Electrical charge	Reflected light	Sound waves
Common location	Side, rear or front button	Under display	Under display
Requires scanner light	No	Yes	No
Direct physical sensor	Usually yes	No	No
Relative cost	Low to moderate	Moderate	Usually higher
Common phone range	Budget to premium	Budget to premium	Mostly premium
Works in darkness	Yes	Yes, using its own light	Yes
Screen protector concerns	Usually low	Possible	Possible
Fingerprint detail	Surface pattern	Two-dimensional image	Detailed depth map
Main strength	Speed and reliability	Affordable in-display design	Advanced under-display scanning

Types of Fingerprint Sensors Based on Their Position

Fingerprint sensors can also be grouped according to where they are placed on a phone.

1. Front-Mounted Fingerprint Sensor

A front-mounted fingerprint sensor is placed on the front of the phone, usually inside a physical home button or front bezel. It was common on older smartphones with large top and bottom bezels.

Benefits:
Easy to use while the phone is lying on a table Clearly visible Can also work as a home button Convenient for one-handed use

Limitations
Takes up space on the front of the phone Reduces the available display area Rarely used in modern full-screen phones

2. Rear-Mounted Fingerprint Sensor

A rear-mounted sensor is placed on the back of the phone, usually near the camera area. It normally uses capacitive technology.

Benefits:
Your index finger naturally reaches the sensor while holding the phone. It can unlock the phone quickly. It does not take up front display space. It is normally reliable and affordable.

Limitations
It is difficult to use while the phone is lying on a table. You may accidentally touch the camera instead. The position may be less comfortable for users with smaller or larger hands. Thick cases can make the sensor harder to reach.

3. Side-Mounted Fingerprint Sensor

A side-mounted fingerprint sensor is usually built into the phone’s power button. Most side-mounted scanners use capacitive technology.

Benefits
It combines the power button and fingerprint sensor. Your thumb naturally rests on it while holding the phone. It can unlock the phone very quickly. It works with LCD and OLED displays. It helps manufacturers create thin phone designs.

Limitations
The narrow sensor area may require careful finger placement. It may be uncomfortable for left-handed users on some phones. A phone case may block part of the sensor. The phone may unlock accidentally when you only want to check the screen.

4. In-Display Fingerprint Sensor

An in-display fingerprint sensor is placed underneath the phone’s screen.

It may use:

Optical technology
Ultrasonic technology

Most in-display readers are designed to work with OLED or AMOLED screens because these display technologies allow the required light or signal to pass through specific areas.

Benefits
It creates a clean and modern phone design. It keeps the sensor on the front of the phone. It is easy to use when the phone is on a table. It removes the need for a separate physical fingerprint button.

Limitations
It may be slower than a good physical capacitive sensor. The scanning area may be difficult to find when the screen is off. Screen protectors can affect recognition. Repairs may be more complicated if the display becomes damaged. The user may need to press more firmly.

Does a Screen Protector Affect the Fingerprint Sensor?

A screen protector may affect an under-display fingerprint sensor depending on its thickness, material, and fit.

Google and Samsung both warn that some screen protectors can reduce fingerprint recognition performance.

To reduce fingerprint problems:

Install a screen protector compatible with your device model.
Check that the screen protector is compatible with your phone’s in-display fingerprint sensor.
Make sure there are no air bubbles over the fingerprint sensor area.
Make sure the screen is clean before registering your fingerprint.
Re-register your fingerprint after installing a screen protector.
Replace a scratched or damaged screen protector.

Why Does a Fingerprint Sensor Fail to Recognize a Finger?

A fingerprint sensor may fail because of:

Wet fingers
Very dry skin
Oil or dirt on the fingertip
Dirt on the sensor
Incorrect finger placement
A damaged screen protector
Cuts or scratches on the finger
A damaged sensor
Poor fingerprint registration
Software problems
A phone case blocking a side sensor

How to Improve Fingerprint Recognition

Follow these practical tips to make your fingerprint sensor work better:

Register your finger carefully: Move your finger slightly during registration so the phone captures the centre, sides, and tip of your fingerprint.
Add more than one finger: Register fingers from both hands so you have another option if one finger is wet, dirty, or unavailable.
Keep the sensor clean: Wipe the physical sensor or fingerprint area with a clean, soft cloth.
Keep your finger clean and dry: Remove any water, oil, or dirt before scanning to improve recognition.
Use a compatible screen protector: Choose a protector that is compatible with your phone’s fingerprint sensor.
Register again after adding a protector: Re-register your fingerprint if recognition becomes less reliable after installing a new protector.
Install software updates: Manufacturers may improve fingerprint recognition through software updates.
Place your finger correctly: Cover the sensor fully and keep your finger still until the phone responds.

Common Fingerprint Sensor Myths

There are several common myths about fingerprint sensors. Let’s clear up some of them.

Myth 1: Every In-Display Sensor Is Ultrasonic

This is incorrect. In-display fingerprint sensors can be optical or ultrasonic.

Myth 2: Every Physical Sensor Is Outdated

A physical capacitive sensor may still be faster and more reliable than a low-quality in-display sensor.

Myth 3: Ultrasonic Sensors Always Work Through Every Protector

A thick or incompatible screen protector can also interfere with an ultrasonic sensor.

Myth 4: The Phone Stores a Normal Photo of Your Finger

This is not usually how fingerprint authentication works. Modern fingerprint systems create and compare a fingerprint template rather than storing a normal photo of your finger. The fingerprint data is typically protected by the phone’s security system.

Myth 5: Fingerprint Unlock Replaces the PIN Completely

Fingerprint unlock does not replace your PIN, password, or passcode. Phones may still require a backup security method after a restart, several failed fingerprint attempts, or certain security-sensitive actions.

Conclusion

Capacitive, optical, and ultrasonic fingerprint sensors all help protect mobile phones, but they scan fingerprints in different ways.

Capacitive sensors use electrical signals, optical sensors use light, and ultrasonic sensors use sound waves. The best option depends on your budget, preferred sensor position, and expected performance.

In my opinion, capacitive sensors are still the best choice for users who want speed and reliability, while ultrasonic sensors are better for people who prefer advanced in-display technology.

Always check real user feedback and phone reviews before making your final decision.