LiDAR, Radar and Ultra-Wideband: How Devices Sense Their Surroundings

Phones, cars, vacuum cleaners and speakers increasingly "know" what's around them: how far away a wall is, whether someone is in the room, where your keys are. They do it with a handful of sensor types, each with different strengths. Understanding them explains what devices can and can't do, and what they might be collecting.

Cameras with computer vision

How it works: software analyzes camera images to recognize objects, faces, text and movement.

Where you'll find it: phone cameras that detect scenes and faces, doorbell cameras that distinguish people from cars, robot vacuums that avoid socks and pet mess, and car systems that read speed limit signs and lane markings.

Limitations: cameras depend on light and can be confused by glare, darkness or unusual objects. They also capture the most personal information of any sensor type.

LiDAR

How it works: LiDAR sends out pulses of laser light and measures how long they take to bounce back, building a map of distances.

Where you'll find it: Apple added a LiDAR scanner to the iPhone 12 Pro in 2020, improving autofocus in low light, augmented reality and room measurement. Many robot vacuums use a spinning LiDAR sensor on top to map rooms. Some self-driving systems, including Waymo's, rely heavily on LiDAR.

Limitations: heavy rain, fog and snow can scatter the light, and high-resolution units have been expensive, though prices have fallen sharply.

Radar

How it works: radar uses radio waves to detect objects and measure their speed, and works in darkness and bad weather.

Where you'll find it: adaptive cruise control and automatic emergency braking in cars, and some smart home devices that detect presence or monitor sleep without cameras. Google put a tiny radar chip called Soli in the Pixel 4 phone in 2019 to detect hand gestures; it was later used in a Nest Hub display for contactless sleep tracking.

Limitations: lower resolution than cameras or LiDAR, so it's better at knowing something is there than at identifying exactly what it is.

Ultrasonic sensors

How it works: like a bat's echolocation, these send out sound above human hearing and listen for echoes.

Where you'll find it: parking sensors in car bumpers, some robot vacuums and simple distance-measuring tools.

Limitations: short range and low detail. Tesla removed ultrasonic parking sensors from its cars in 2022 and 2023 in favor of camera-only systems, a change that drew complaints when the camera system initially performed worse for parking.

Ultra-wideband (UWB)

How it works: UWB radio measures the travel time of signals between devices very precisely, locating them to within centimeters.

Where you'll find it: Apple's AirTag and "Precision Finding," which points you toward a lost item; some Samsung SmartTags; and digital car keys that unlock a car as you approach and prevent relay attacks used by thieves.

Limitations: short range and only works between devices that both support it.

Motion, light and environmental sensors

Almost every phone contains an accelerometer and gyroscope (to detect movement and orientation), a magnetometer (compass), a barometer (altitude, used for counting floors climbed), an ambient light sensor and a proximity sensor that turns off the screen during calls. Smart thermostats use occupancy and humidity sensors to adjust heating automatically.

Sensors in health and wellbeing devices

Smartwatches combine optical heart sensors, accelerometers and temperature sensors to estimate heart rate, activity and sleep. Some phones and tablets use their cameras to measure heart rate from a fingertip. Hearing aids and some earbuds use microphones and motion sensors to adjust to noisy environments and detect falls. These are convenient, but readings are estimates, and medical decisions need medical-grade devices.

Sensors in cars beyond safety systems

Cars increasingly watch the driver as well as the road. Driver monitoring cameras track eye and head position to detect drowsiness or distraction. European Union rules now require new cars to warn drivers who are drowsy or distracted, and many manufacturers meet that requirement with these cameras. Rain sensors on the windshield switch on wipers automatically, light sensors control headlights, and seat sensors detect occupants for airbag and seatbelt reminders. Some cars now include sensors that detect a child left in the back seat and sound an alert.

Smart speakers and presence detection

Smart speakers and displays use microphones constantly listening for a wake word, processed on the device before anything is sent to the cloud. Some models also use ultrasound, radar or Wi-Fi signals to detect whether someone is in the room, which lets them turn on displays or trigger routines automatically. Most offer settings to turn off these presence features and to delete stored voice recordings.

Sensor fusion

Most capable devices combine several sensors so each covers the others' weaknesses. Cars with advanced driver assistance often pair cameras with radar. Phones combine GPS, Wi-Fi, motion sensors and the barometer to estimate location indoors, where GPS signals are weak. This combining is called sensor fusion and is why devices have become more reliable at understanding their surroundings.

What it means for privacy

• Check what's processed on the device. Some products analyze sensor data locally; others upload it to the cloud. Local processing is generally more private.
• Look for physical controls. Camera shutters and microphone mute switches give certainty that a sensor is off.
• Review app permissions. Phones let you limit which apps can access the camera, microphone, precise location and nearby devices.
• Be aware of tracking misuse. After reports of tracking tags being used to follow people, Apple and Google added alerts that warn you if an unknown tracker is moving with you, and agreed in 2024 on a shared standard so alerts work across iPhone and Android.

Where it's heading

Sensors keep getting smaller, cheaper and more power-efficient, and more processing happens on dedicated chips in the device. Expect more homes and cars that respond to presence and gestures, and more debate about how much sensing people are comfortable with in private spaces.