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What's the deal with radar on a phone anyway?

The radar-powered sensor on Google's Pixel 4 phone is the first to appear on a phone, ever. Here's what that really means.

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The Pixel 4 is the first phone to use radar.

Sarah Tew/CNET

Google's new Pixel 4 represents the first time that radar has appeared on any mobile phone. On the Pixel 4, it powers a motion sensor that Google uses to drive a suite of features, including gestures to control the device hands-free, and faster face unlock (but there's a big caveat here). Google aptly calls the sensor Motion Sense.

Phone-makers have experimented with motion control for years, using the camera sensor to know where you are and interpret what it is you want to do hands-free, like swipe through photos in a gallery and switch tracks in a music app. Some, like the LG G8, have even concocted elaborate motions to launch certain apps by pinching your fingers into a bird's beak, or adjust audio by miming a turn of a dial. 

The missing ingredient in these clunky earlier tests, at least according to Google, is radar, which the company hopes will make motion sense quick and convenient to use when it comes to your phone knowing where you are.

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Radar isn't what makes face unlock work

Before we get into anything else, know that radar isn't the same as face unlock. Google Motion Sense understands when you're reaching for the Pixel 4 and lights up the screen, bracing for your face to come into range and do the rest. But that's all the radar-fueled chip inside does. The sensor, which Google calls Soli, isn't actually scanning your mug to make sure you're really you.

For that, Google relies on an infrared camera to project dots on your face, just like Apple uses in the iPhone ($699 at Amazon) for Face ID. We're not sure how many dots are being projected onto your face (we asked), but it's this depth map that does the actual unlocking. Motion Sense just speeds up the process so you don't have to swipe to unlock the phone, or even pick it up to trigger raise-to-wake.

What Motion Sense does on the Pixel 4

Motion Sense can detect your presence, if you're reaching for the phone and gestures that have you decisively swipe left or right with your hand. With Motion Sense enabled, you can:

  • Swipe to advance musical tracks back and forth, as with the YouTube Music app
  • Swipe to dismiss an incoming call or to dismiss an alarm or timer
  • Trigger the Pixel 4 screen to wake up as you reach for the device (to enable faster face unlock)
  • Reduce the volume of an alarm or timer as you reach toward the phone
  • Trigger the phone to turn the screen off as you walk away
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How radar works on the Pixel 4

Google chose radar for Motion Sense, rather than relying on the camera to "see" you, because of its longer range and low use of power. Radar uses radio waves to sniff out the size, location and proximity of objects. While you can turn off any of the Motion Sense features on the Pixel 4 (individually or all together), if Motion Sense is enabled, it's always detecting you. 

Google says that its technology uses a 60GHz radio frequency, doesn't travel very far and has passed all requisite safety requirements.

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This is how Google visualizes the Pixel 4's Soli radar sensor to detect your presence and motion.

Sarah Tew/CNET

Radar's range

The Pixel 4's chip has a 180-degree field of view, which means that it has spatial awareness everywhere in front of it and off to the sides. In terms of depth -- how far in front of the phone it's sensing -- a Google rep told me that it's looking at least 0.6 inch (about 1.1 cm) in front of the phone face for presence, and detects gestures at nearly a foot (30 cm) away from the sensor.

Radar and privacy

To quell privacy concerns over the use of radar in the Pixel 4 phone, Google confirmed at its launch event that all radar data is stored locally on the device, and not on Google's servers. Radar, too, isn't distinct enough to pick up a detailed picture of your hands or face, for example. The Soli sensor is tuned to look for blobs of mass and motion, not people.

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The new Pixel 4 could inspire other phones to ratchet up their motion-sensing game.

Angela Lang/CNET

Will Google add more gestures to Motion Sense?

The company's keeping quiet about future plans, including if it will add a radar sensor to the back of the phone as well. A rep did say, however, that Google could potentially use Soli's ambient awareness to boost your productivity on the phone and build out a larger gesture vocabulary.

Will other phones get radar, too?

When Google does anything, rivals pay attention. Google's Android OS powers roughly nine out of 10 smartphones on the planet, but it's likely that the company wants to keep its Motion Sense and secure face unlock secrets to itself. (It even developed its Titan M chip on top of Qualcomm's base to add its own layer of security.) 

That said, it'd be easy to see other phone-makers pursue both a better system of gesture control than using the camera to sense you, as well as the level of secure face unlock found in the Pixel 4, a feat few have accomplished.

There's much more to learn about the Pixel 4's specs, looks and features, including a bundle of new camera improvements that promise incredible low-light prowess and how it compares to its biggest rival phones you can buy now. Here's everything Google announced at its event this week.

Originally published earlier this week.