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Fingerprint unlocking isn't just for your phone

New smart locks are putting your door's security at your fingertips.

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James Martin/CNET

Fingerprint unlocking, with all its flaws and sensitivities, is an increasingly popular way to unlock your smartphone. That method is headed to your front door, too. Smart locks are beginning to incorporate fingerprint sensors. We tried out two models you can buy right now at the CNET Smart Home to get a feel for what unlocking your door with your digits is really like. 

How fingerprint readers work

Fingerprint readers come in different types. There are three commonly-used fingerprint reading methods: capacitive, ultrasonic and optical. Each one captures and reads your fingerprint a little bit differently. Here's a quick rundown.  

Optical

Optical fingerprint readers use LED light beneath a glass plate to illuminate your fingerprint and capture an image. The ridges and valleys in your fingerprint translate to light and dark areas in the image. Once the reader stores an image of your print, it uses that record as a template to compare and look for future print matches. 

Because optical sensors are easily affected by dirt, oil or odd lighting, it isn't the most secure type of fingerprint reader out there. 

Capacitive

Capacitive readers measure electrical current to sense your fingerprint's image instead of light. Human skin is conductive, and the capacitive sensor is able to measure the smallest differences in conductivity caused by the ridges and valleys of your print. A small voltage can be applied by some capacitive sensors to enhance the electrical signal for an image with better contrast. 

Capacitive fingerprint readers resist contamination better than optical readers. It's harder to fool this scanner using a high-quality fingerprint photograph. However, you could technically fool a capacitive reader with a replica or 3D mold of a person's fingertip (ew).

Ultrasonic 

Ultrasonic fingerprint readers use high-frequency ultrasonic sound to read your fingerprint. You won't be able to hear it, but these tiny sound waves map out the details of your finger's ridges and valleys. The scanner captures fingerprint details with a transmitter and receiver system.

An ultrasonic pulse is transmitted against the finger placed over the scanner. Some of this pulse's pressure is absorbed and some is bounced back to the sensor, depending on the depth of ridges, pores and small details unique to each fingerprint. The result is a 3D reproduction of the fingerprint.

The 3D details are much more difficult to forge, making the ultrasonic system more secure than capacitive or optical. Ultrasonic sensors are what you'll find beneath phone screens like the Samsung Galaxy S10

Smart locks with fingerprint readers

Fingerprint locks are gathering steam in the market, and the two models we tested use a capacitive fingerprint reader. Let's take a closer look at how these locks work in the real world.

Tyler Lizenby/CNET

The Ultraloq U-Bolt Pro includes a front capacitive fingerprint sensor. Like most smart locks, it replaces your existing deadbolt. You'll need a screwdriver and about 15 minutes to get the U-Bolt Pro on your door.

The U-Bolt Pro comes in black and silver and costs $200. A $230 bundle adds the Wi-Fi bridge to enable remote access. I tested the bundled Wi-Fi package at the CNET Smart Home.  

There are six ways to unlock your door with the U-Bolt Pro: fingerprint, physical key, a feature called "Magic Shake", auto unlock, keypad codes and a companion smartphone app. On the lock's exterior, a keypad surrounds a central fingerprint reader and an Ultraloq logo button at the bottom locks the door when pressed.

If you're not opting to use the fingerprint reader, or if you want a bit of extra protection when you use a keypad code, you can enter random numbers before or after your passcode. You'll set that up in the U-Bolt app. There's also a cleverly hidden physical keyhole behind the keypad. A hinge at the bottom opens up the face of the lock so you can use your key. 

On the interior side, a battery pack holds four AA batteries. You can view battery status and receive notifications when power is low in the U-Bolt app. However, if your batteries do die completely, there's a Micro-USB port on the outside of the lock for emergency power. Plug it into a power bank for instant functionality.

The U-Bolt Pro supports access for up to 95 users or 95 fingerprints on what it calls a "360-degree Live Capacitive Sensor." It works with Amazon Alexa and Google Assistant for voice unlocking. One thing to note here with voice commands: Alexa requires a PIN to unlock the door. Google does not. It's always a good idea to use a PIN when voice unlocking. 

Ultraloq says that your data is encrypted with two-layer protection with a 128-bit AES and dynamic keys, a method of encryption that uses unique one-time cryptographic patterns to protect data. 

This lock certainly isn't winning any awards for beautiful design, but it is very functional, has plenty of options and customizations for how to access your door and is well within most smart lock price points even at $230. 

Tyler Lizenby/CNET

This fingerprint sensing smart lock takes a more design-focused approach to protecting your door. A shiny touchscreen interface greets you at the front door, and a barely noticeable fingerprint scanner sits on the side. 

Lockly Secure Plus is available from major retailers like Home Depot, Lowe's and Best Buy for $200. Upgrade to the Lockly Secure Pro with Wi-Fi Module and you'll pay $300 to control your smart lock from anywhere.

Lockly Secure Pro comes in three finishes: satin nickel, venetian bronze and matte black. There's a latch option with a door handle and a deadbolt option with a thumb turn on the interior side.

The Lockly app is where you can set user codes, manage auto lock settings and link your lock to voice assistants. Lockly Secure Pro can hold up to 99 fingerprints. 

You'll have five ways to unlock a door with Lockly installed: keypad, 3D fingerprint sensor, Lockly app, Alexa or Google Assistant voice commands and traditional key. You'll need a PIN code to unlock via voice with either assistant.

Should you buy one? 

We haven't seen nearly as many fingerprint smart locks as we have keypad, touchscreen and Bluetooth models. It's still an emerging sub-category of smart lock. That said, we can't recommend that you dive head first into putting biometrics on your front door. 

"The upside to biometrics is that they make security really easy," Ted Harrington, Executive Partner at Independent Security Evaluators notes. "Think about when the iPhone introduced the fingerprint reader; many people who otherwise didn't lock their phones now started to, because it was so easy. That was a major improvement in security."

Harrington points out that it all comes down to how the system is designed. If developers don't properly implement the ability to revoke access, or if they accidentally make it easy to bypass authentication, then the fingerprint capability becomes just an added weakness. 

"You are giving your biometrics to a private company. They can do anything they want with it, monetize it in any way they want," said Harrington. "You cannot change your fingerprint, so that's a pretty permanent decision you are making." 

Nothing is as uniquely you as your fingerprint, and if enough companies can get this right, there's something to be said for unlocking your home with your fingerprints. If they can't, it poses a larger risk about biometric data. 

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