Biometric authentication has become a core part of the modern smartphone experience, and fingerprint sensors remain one of the most widely used security features today. While facial recognition has gained popularity, fingerprint unlocking continues to be favored for its speed, reliability, and simplicity. As smartphone designs have evolved, so too have fingerprint sensor placements, with two dominant options emerging: in-display fingerprint sensors and side-mounted fingerprint sensors.
Both technologies aim to achieve the same goal—fast and secure authentication—but they approach it in very different ways. This article provides an in-depth, real-world comparison of in-display and side-mounted fingerprint sensors, focusing on accuracy, speed, reliability, usability, and everyday practicality.
A Brief Evolution of Fingerprint Sensors
Fingerprint sensors were first introduced on smartphones as physical buttons, often embedded in the home key or placed on the back panel. These early implementations were praised for their speed and consistency. However, as phones moved toward bezel-less designs and larger displays, manufacturers sought alternatives that would preserve aesthetics without sacrificing functionality.
In-display fingerprint sensors emerged as a solution, allowing authentication hardware to sit beneath the screen. At the same time, side-mounted fingerprint sensors gained popularity by integrating biometric scanning into the power button. Each approach reflects a different balance between design priorities and user experience.
How In-Display Fingerprint Sensors Work
In-display fingerprint sensors are embedded beneath the smartphone’s screen, typically using either optical or ultrasonic technology. Optical sensors work by illuminating the finger and capturing an image of the fingerprint pattern, while ultrasonic sensors use sound waves to create a 3D map of the fingerprint.
Optical sensors are more common in midrange and budget devices, while ultrasonic sensors are usually found in premium models. Ultrasonic technology generally offers better security and performance, especially with wet or dirty fingers.
One of the main advantages of in-display sensors is aesthetic. They allow manufacturers to create clean, uninterrupted designs without visible biometric hardware. However, placing a sensor beneath the display introduces challenges related to accuracy, speed, and consistency.
How Side-Mounted Fingerprint Sensors Work
Side-mounted fingerprint sensors are typically integrated into the power button, allowing the same physical component to handle both locking and unlocking the device. These sensors rely on capacitive fingerprint technology, which has been refined over many years.
Capacitive sensors read the ridges and valleys of a fingerprint through electrical signals, making them highly accurate and responsive. Because they are not hidden beneath layers of glass, side-mounted sensors often deliver faster and more consistent results.
From a design perspective, side-mounted sensors strike a balance between minimalism and functionality. They are discreet, intuitive, and do not interfere with screen design.
Accuracy: Which Sensor Gets It Right More Often?
Accuracy is arguably the most important factor when evaluating fingerprint sensors. A sensor that fails to recognize authorized users or mistakenly accepts incorrect fingerprints undermines both convenience and security.
In real-world testing, side-mounted fingerprint sensors generally demonstrate higher accuracy rates. Their capacitive nature allows them to capture detailed fingerprint data quickly, even with slight variations in finger placement. They tend to perform reliably across a wide range of conditions.
In-display sensors, particularly optical ones, can be more sensitive to finger positioning and environmental factors. Users often need to place their finger precisely over the marked area on the screen, and slight misalignment can result in failed scans. Ultrasonic sensors perform better in this regard but are not immune to occasional inconsistencies.
Overall, side-mounted fingerprint sensors have a slight edge in accuracy, especially for users who unlock their phones frequently throughout the day.
Speed and Responsiveness
Speed plays a crucial role in user satisfaction. The best fingerprint sensor is one that works almost instantly, without requiring conscious effort or repeated attempts.
Side-mounted fingerprint sensors are typically faster. Because the finger naturally rests on the power button when picking up the phone, authentication often happens before the screen even turns on. This seamless interaction creates the impression of instant unlocking.
In-display sensors require the screen to be active and the finger to be placed on a specific area. While modern implementations have improved significantly, there is still a noticeable delay compared to side-mounted sensors, especially on devices using optical technology.
For users who prioritize speed and efficiency, side-mounted fingerprint sensors offer a more fluid experience.
Reliability in Different Conditions
Everyday use exposes fingerprint sensors to a variety of conditions, including wet fingers, dry skin, dirt, and sweat. How well a sensor handles these variables is critical to its reliability.
Side-mounted capacitive sensors tend to perform consistently across different conditions. While extremely wet fingers can still cause issues, these sensors are generally forgiving and adaptable.
In-display optical sensors struggle more with moisture and smudges. Wet fingers can distort the optical image, leading to failed authentication attempts. Ultrasonic sensors perform better in challenging conditions, as they rely on sound waves rather than light, but they are still not flawless.
In terms of overall reliability, side-mounted sensors maintain a noticeable advantage for users with active lifestyles or those frequently exposed to varying environments.
Ergonomics and Ease of Use
Ergonomics significantly influence how natural a fingerprint sensor feels during daily use. Placement matters, especially for users who unlock their phones dozens of times per day.
Side-mounted fingerprint sensors are easy to reach and intuitive. The act of pressing the power button naturally aligns the finger with the sensor, reducing the need for deliberate positioning. This design works well for both right-handed and left-handed users, depending on phone orientation.
In-display fingerprint sensors require users to adjust their grip and place their finger on a specific area of the screen. While this becomes habitual over time, it is less intuitive, especially when unlocking the phone with one hand.
When it comes to one-handed use and quick access, side-mounted sensors generally feel more ergonomic.
Security Considerations
Security is another critical factor when comparing fingerprint sensor technologies. Both in-display and side-mounted sensors offer strong protection when implemented correctly, but there are differences worth noting.
Ultrasonic in-display sensors are considered highly secure due to their ability to capture three-dimensional fingerprint data. This makes them more resistant to spoofing attempts using images or molds.
Optical in-display sensors, while still secure for everyday use, are theoretically more vulnerable to sophisticated spoofing techniques. However, such attacks are rare and unlikely for most users.
Side-mounted capacitive sensors have a long track record of reliability and security. They are difficult to fool and remain one of the most trusted biometric solutions available.
For typical smartphone users, both options provide sufficient security, but ultrasonic in-display sensors and capacitive side-mounted sensors represent the highest standards currently available.
Impact on Design and Durability
Fingerprint sensor placement also affects overall device design and durability. In-display sensors allow for uninterrupted designs and larger screens, which appeal to users who value aesthetics.
However, in-display sensors rely heavily on screen integrity. Cracks, screen protectors, or display replacements can sometimes interfere with sensor performance.
Side-mounted sensors are more isolated from the display and less affected by screen damage. They also work reliably with most cases and screen protectors, making them a practical choice for long-term durability.
Real-World User Preferences
User preference often depends on familiarity and usage habits. Users transitioning from older phones with physical fingerprint sensors often find side-mounted options more comfortable and dependable.
On the other hand, users drawn to modern, bezel-less designs may prefer in-display sensors despite their occasional limitations. Over time, muscle memory adapts, and many users become comfortable with either option.
That said, feedback consistently highlights side-mounted fingerprint sensors as being more reliable and less frustrating in everyday use.
Final Verdict: Which Fingerprint Sensor Is Better?
After testing and comparing in-display and side-mounted fingerprint sensors across accuracy, speed, reliability, ergonomics, and security, a clear pattern emerges.
Side-mounted fingerprint sensors offer superior accuracy, faster response times, and greater reliability in real-world conditions. Their intuitive placement and consistent performance make them an excellent choice for users who prioritize efficiency and dependability.
In-display fingerprint sensors excel in design aesthetics and innovation, particularly ultrasonic variants found in premium devices. While they have improved significantly, they still require more precise interaction and can be less forgiving under certain conditions.
Ultimately, the best fingerprint sensor is the one that fits your usage habits and priorities. If you value speed, accuracy, and practicality, side-mounted sensors remain the most reliable option. If design and cutting-edge technology matter more, high-quality in-display sensors can still deliver a satisfying experience.
As smartphone technology continues to evolve, fingerprint sensors will undoubtedly improve further. For now, understanding the strengths and weaknesses of each approach helps users make informed decisions and set realistic expectations for daily use.
