BIOMETRICS FACE THE FACTS

Today's devices can log you in instantly with a fingerprint or a smile. But how do biometric technologies work, and can they really be relied upon?

- Darien Graham-Smith finds out

Passwords have become rather old hat.

In fact, there are moves afoot to ditch them altogether in favour of all-digital passkeys, but for those to work you still need some way to prove your identity. And that's where biometrics come in.

The word literally means measuring biology, and most modern biometric systems are based on the age-old detective technique of identifying someone by their fingerprints, or the even older social technique of recognising a person by what their face looks like. There are plenty of other ways to identify somebody from their bodily characteristics, such as by analysing their voice, examining the blood vessels at the back of their eye or even decoding their DNA – but for consumer devices, fingerprints and facial recognition technologies fit the bill nicely, as they're cheap, quick, unobtrusive and fairly secure.

Since these things are now ubiquitous in our daily lives, you might well wonder: how do they actually work, and should we be relying on them so much?

Prints of peace

Fingerprint readers come in three main types: capacitive, optical and ultrasonic. A capacitive reader is the sort that might be built into the power button on your laptop or a panel on the back of your phone. When you put your finger on it, a tiny current is induced, which can be detected and measured by the device.

The technology is similar to the way a touchscreen works, except that while a typical phone screen only has to register the location of a tap to an accuracy of around half a millimetre, a fingerprint reader is designed to work at a scale of hundredths of a millimetre. And rather than just detecting whether a touch is present or not, a capacitive fingerprint reader measures how the current changes across the sensor's surface, enabling it to map out the individual ridges and valleys of your fingertip.