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Home Latest Articles Smartphones Kagoo Explains - Smartphone Biometrics

Kagoo Explains - Smartphone Biometrics

Updated 22 April 2021
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Kagoo recently started supporting smartphones on the site, offering comprehensive details on a whole range of quality smartphones. You can browse all the latest Smartphones in our Smartphone Hub & view the best deals on our Smartphone Deals Page. To celebrate their arrival, we’re looking in depth at smartphone features - today we’re looking at security features, and how your fingerprint or face is used to keep your phone locked.

For many people a smartphone is the cornerstone of their life - that little rectangle holds a wealth of private information including addresses, banking details, passwords and more. It’s therefore crucial to protect this data from unwanted intrusion, and make sure only the user can gain access. This article concerns the most recent technology for smartphone security - Biometric Authentication.

Biometrics are defined as the measurements and characteristics of human bodies (height, weight, eye colour, etc). Within these are ‘biometric identifiers’ - specific markers which are unique from person to person, such as fingerprint pattern, voice, DNA or the configuration of a face. These characteristics can be used to identify individual humans, and therefore make a powerful basis of smartphone security.

Two major form of biometric authentication are currently used in smartphones - fingerprint scanning and facial recognition. Let’s take a look at both of these in detail:

Fingerprint Scanning


If you’ve ever watched a crime drama for more than 10 minutes, you’ll know that even a small fingerprint on a bit of evidence would be enough for the baggy-jumper-wearing, doesn’t-play-by-the-rules, emotionally-broken detective to crack a case wide open. That’s because the pattern of ridges that make up the surface of your fingers are unique - while they may share similar characteristics, no two are absolutely identical.

This makes fingerprints perfect for smartphone security - especially since you’re usually holding your phone when using it. There are numerous different styles of fingerprint scanners, but the goal remains the same - ascertain whether the finger trying to unlock the phone matches any of the fingerprints authorised by the system.

The earliest versions of fingerprint scanners were optical - that is, they captured an image of the finger pressed to the sensor, compared it to the stored photo, and ascertained whether it was a match. While simple and cheap, these systems had severe limitations - because they could only use a 2D image for analysis, there was a limit to how detailed the check could be. The system may only look for the vaguest similarity between fingerprints, leading to false matches. Even more troubling, it was possible to spoof the scanner with a high-quality photo of a fingerprint pressed against the scanner.

Smartphones then moved to ‘capacitive scanners’ for increased security. These used an array of components called ‘capacitors’, which can detect when a conducting material (such as human skin) is pressed against it. This stops people fooling the system with a 2D photo, and allows for far more detailed ‘scan’ of the fingerprint to be created - decreasing the chances of a false match. While these scanners were originally very expensive, improved production methods and cheaper materials have made them a mainstay in modern smartphones.


Both of the above methods require a dedicated button or area on the phone - the ubiquitous circle at the bottom of earlier iPhones. While easy to reach, the size required for the device eats into the space available for the screen. This is where ultrasonic scanners come in - these fingerprint scanners send out ultrasonic waves, and track the waves bounced back. Using this the phone can build up a highly-detailed ‘map’ of a finger - and it can be built into the screen of a phone. This allows smartphone manufacturers to maximize the space on the device - though at a cost. Ultrasonic scanners are significantly slower than capacitive scanners, and the technology is more expensive. So far it has seen scattered adoption across modern smartphones - though some companies are betting this is the future of smartphone security.

Fingerprints are a secure and safe method of securing your smartphone, but there are limitations to the system. Obviously, you have to have your fingers available to use the scanner - this means you can’t unlock it hands-free, and can’t be wearing gloves or other coverings. The scanning can also be impeded if your hands are greasy or wet - which can be frustrating when using your phone in the rain or while cooking!

Other methods of smartphone security

Apart from biometric scanning, there are several other methods of security used in smartphones. Early smartphones used a proper password system, similar to that of a computer. This was unwieldy, due to the frustrations of typing on a smartphone keyboard. This then moved to a PIN (Personal Identification Number) system, similar to those used in bank cards. This is a popular security method, and still used as a backup in most smartphones for times when the biometrics.

The pattern is another popular method, used extensively in earlier Android phones. This asked people to create a pattern of swipes on a grid instead of a password - the idea being a symbol was easier to remember and harder to spoof than a pin. This method has largely been retired now, and replaced with biometrics or a PIN.

Facial Recognition

Facial recognition is the other major form of biometric identification used in smartphones. It is a newer technology - though the first smartphone with facial recognition capabilities was unveiled in 2005, they were rarely used - and nowhere near as effective as fingerprint scanning - until Apple launched the iPhone X in 2017. Since that point, facial recognition has become a standard in modern smartphones, though some devices offer both facial and fingerprint scanning, to allow users a choice of security methods.

Facial recognition, as the name suggests, uses the makeup of an individual’s face to identify them. In practice, your phone will send out a large amount of invisible infrared ‘dots’ across your face, then a special processor uses these to map the ‘geometry’ of your face, measuring the space between your eyes, length from nose to mouth, facial width, etc. The system then uses these to build a unique ‘map’ of your face, known as a ‘facial signature’. This signature is then stored, and any entry attempts are compared against the stored signature - if they match, then the phone unlocks!

Facial Recognition vs Iris Recognition

While some facial recognition systems scan an entire face, others only scan your eyes - using the unique pattern of your irises in much the same way as a fingerprint scanner. Sometimes the difference will be marked, but there have been cases of iris scanning being advertised as ‘full’ facial recognition. It shouldn’t make a large difference to the average user though - the method and results are largely the same.

As with fingerprint scanning, while there may be numerous similarities between people, no 2 faces will be absolutely 100% identical in measurements. In theory, even the smallest difference will be detected by the system - making the system very secure against intruders. However, there have been a number of cases of people managing to spoof facial recognition - the question of how much these systems pick up on unique differences is hotly debated, with hackers claiming to gain access with 2d composites of facial features, or even tricking the system with a 3D printed version of a human head! Moreover, while Apple claims that the chance of someone else being able to unlock your phone is “1 in a million”, it seems that identical twins may defeat the system.

Facial recognition can also have problems giving accurate readings while wearing a mask (which is a particular trouble these days) or in low-light conditions.


However it’s important to remember that the systems are being constantly iterated and improved - Apple’s FaceID system uses an infrared ‘floodlight’ to allow the system to work even in darker rooms, and improvements to facial recognition algorithms over the last year have lessened the problems of masks confusing the system. The security of facial recognition is constantly improving - much like fingerprint technology was several years ago.

Facial recognition is a new and evolving technology, and while it isn’t quite as secure as fingerprints just yet, it has several important benefits. Since there is no need to physically interact with the phone, it means you can unlock your phone hands-free or from a distance. Extremely helpful when you’ve got your hands full, or when your phone is just out of reach. It also stops the problem of the phone not recognising your fingerprints due to greasy or wet fingers. Finally, it’s just far far more convenient - why take off your gloves and press your finger against the device when you can just look at it? Simples!

Problems of biometric authentication

It’s hard to talk about biometric security without touching on the controversies surrounding it. No security system is foolproof, but as we’ve seen there are some rather large security holes in biometric authentication systems that make them easy to spoof if you have the right knowledge.

There are also numerous privacy fears attached to centralised systems scanning fingerprints and faces. The last few years have seen reports on racial profiling issues arising from facial recognition technology being sold to police, and on possibly racial bias lurking in systems from big names such as Amazon, Microsoft and IBM. There is concern about whether technology companies and governments can be trusted to police themselves with this technology. We constantly see reports of tech firms selling personal data to anyone who’s interested, and there is the scary possibility of a mass surveillance program using smartphone biometrics as the backbone. Indeed the EU is currently trying to block AI & biometric mass surveillance systems to try and head off such a future.

These criticisms and troubles of biometric security are very valid, but the fact remains that this technology is commonly used in consumer technology, and isn’t going away anytime soon. While there is a need for strong oversight and restriction on their misuse, both fingerprint and facial recognition technology are helpful and convenient ways of securing your smartphone, and the security and power of these systems will continue to improve with the coming years.

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