Under-Screen vs Physical Fingerprint Scanners
Under-screen fingerprint scanners and physical fingerprint scanners both unlock your phone by reading your fingerprint, but they differ in how they capture the print, where they sit on the device, and how they perform in real-world conditions. Under-screen scanners are built into the display, while physical scanners are separate modules usually on the front, back, or side of the phone. This article explains the technical differences, pros and cons of each, and how to choose between them.
Background: How Fingerprint Scanning Evolved
Fingerprint recognition on phones became mainstream in 2013 with the iPhone 5s, which used a physical capacitive sensor on the front. For years, physical sensors were the standard: they were reliable, fast, and easy to place. As phones moved toward edge-to-edge displays, manufacturers wanted to remove the bezel that housed the front sensor. The solution was to embed the sensor under the display itself, first appearing in 2018 with the Vivo X20 Plus UD and later the in-display sensor on the Samsung Galaxy S10 series. Since then, under-screen scanners have become common on mid-range and flagship Android phones, while Apple has stuck with physical Face ID and Touch ID on the side button for its iPhones.
How Under-Screen Scanners Work
Under-screen scanners use either optical or ultrasonic technology to capture your fingerprint through the display glass.
- Optical scanners shine a bright light through the OLED panel, which reflects off your finger back to a tiny camera sensor beneath the screen. The reflected image is a 2D picture of the ridges and valleys of your print. This is the most common type because it is cheap and works well on OLED displays.
- Ultrasonic scanners emit high-frequency sound waves that bounce off your finger. The sensor measures the time and intensity of the echoes to create a 3D map of the print, including depth. This is more secure and works better with wet or oily fingers, but it is more expensive.
Both types require a thin display module that allows light or sound to pass through, which is why they are only found on OLED screens, not LCDs. The sensor sits directly under the glass, and the phone’s software highlights a specific area on the screen where you must place your finger.
How Physical Scanners Work
Physical scanners are almost always capacitive. They consist of an array of microscopic capacitors that detect the ridges and valleys of your finger when it touches the sensor. The ridges create a different capacitance than the valleys, and the chip converts that pattern into a digital image. Because the sensor is in direct contact with your skin and has a dedicated surface, it can capture a very clear and consistent image every time.
Physical sensors are placed in three common locations:
- Front home button (e.g., older iPhones, Samsung Galaxy S8) – convenient but takes up bezel space.
- Back panel (e.g., Pixel 4a, LG G8) – natural for your index finger but awkward when the phone is on a table.
- Side power button (e.g., iPhone SE, Sony Xperia 5) – works for both left- and right-handed users and doubles as a button.
Performance and Reliability: Which Is Faster and More Accurate?
Physical scanners are generally faster and more accurate than under-screen optical scanners. A physical sensor reads your fingerprint the instant your finger touches it, with no need to light up the screen. Under-screen optical scanners require the display to brighten the sensor area, which adds a fraction of a second and can be fooled by a high-resolution photo of your fingerprint. Ultrasonic under-screen scanners are more secure than optical ones because they read the sub-surface of your skin, making them harder to spoof, but they are still slightly slower than a physical sensor.
In terms of accuracy, physical scanners have a lower failure rate with dry or calloused fingers because the capacitive sensor directly measures the electrical properties of your skin. Under-screen optical scanners struggle with very dry skin and bright sunlight, which can wash out the reflected image. Ultrasonic scanners handle wet fingers better than optical ones, but they can fail if the screen protector is too thick or has air bubbles.
Common Problems and How to Avoid Them
Under-screen scanners have a few well-known issues:
- Screen protectors – A thick or poorly applied screen protector can block the optical sensor. Use a protector specifically designed for under-screen scanners, and re-register your fingerprints after applying it.
- Sunlight – Bright sunlight can interfere with optical scanners. Cupping your hand over the screen or using a different finger often helps.
- Dry skin – Optical scanners rely on light reflection, which is poor when your skin is dry. Moisturizing your hands or breathing on the sensor area can temporarily improve the image.
- Finger placement – You must hit the exact sensor area. If you miss, the phone does not read your print. Physical sensors are larger and easier to hit by feel.
Physical scanners also have issues, but they are less common: a scratched sensor may fail to read, and a dirty sensor can be fixed by wiping it. Since physical sensors are separate, they are not affected by screen brightness or protectors.
Cost and Manufacturing Trade-offs
Under-screen scanners are more expensive to integrate, which is why they are mostly found on mid-range and flagship phones. The sensor itself costs more, and the display module must be custom-designed to allow light or sound to pass through. Physical scanners are cheaper and simpler, which is why budget phones and many mid-range devices still use them. However, the cost difference is small at the component level; the bigger factor is the design choice. A phone with a physical front scanner needs a bezel, which many manufacturers avoid for aesthetic reasons. A back or side scanner is cheaper but less convenient for some users.
Safety and Security: Which Is More Secure?
Physical capacitive scanners are considered more secure than optical under-screen scanners because they are harder to fool with a printed or digital image. Ultrasonic under-screen scanners are comparable to physical ones in security because they read the 3D structure of your fingerprint, including sweat pores and sub-surface ridges. Optical scanners are the least secure, as a high-resolution photo of your fingerprint can sometimes unlock the phone. That said, all fingerprint scanners are less secure than a strong PIN or password, and they can be bypassed with a lifted print. For most users, the convenience outweighs the risk, but if you handle sensitive data, consider using a longer passcode or two-factor authentication.
How to Choose: Which One Is Right for You?
Your choice depends on your priorities:
- Speed and reliability – Choose a physical scanner (side or back) if you want the fastest, most consistent unlock.
- Modern design – Choose an under-screen scanner if you want a full-screen display without a bezel.
- Wet or oily fingers – Ultrasonic under-screen scanners handle moisture better than optical, but a physical scanner is still the most reliable in wet conditions.
- Screen protectors – If you always use a thick glass protector, a physical scanner is safer.
- Budget – Physical scanners are found on cheaper phones, so if you are on a tight budget, you will likely get a physical sensor.
Frequently Asked Questions
Can I use a screen protector with an under-screen scanner?
Yes, but it must be a protector designed for under-screen scanners. Standard thick glass protectors can block the optical sensor. After applying the protector, re-register your fingerprints to ensure the phone can read them through the new layer.
Why is my under-screen scanner not working in sunlight?
Optical scanners rely on the light reflected from your finger. In bright sunlight, the ambient light overwhelms the sensor, making it hard to capture a clear image. Cupping your hand over the screen or moving to shade usually fixes the problem.
Are under-screen scanners slower than physical ones?
Yes, especially optical ones. The sensor needs to light up the screen and capture the image, which adds a few milliseconds. Ultrasonic scanners are slightly faster but still not as quick as a physical capacitive sensor.
Which is more secure: optical or ultrasonic?
Ultrasonic is more secure because it creates a 3D map of your fingerprint, making it harder to fool with a photo. Optical scanners are the least secure of the three types.
Do all under-screen scanners work with wet fingers?
No. Optical scanners often fail with wet fingers because water distorts the light reflection. Ultrasonic scanners handle moisture better but are not perfect. Physical scanners are the most reliable with wet hands.
Why do iPhones not use under-screen fingerprint scanners?
Apple has chosen Face ID for its flagship iPhones and a physical Touch ID button on the iPhone SE. They have not adopted under-screen fingerprint technology, likely due to their preference for Face ID and the cost of integrating a new sensor.
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