Proximity Sensors Do More Than You Think in Today's Smartphones

The most basic example is the sensor that shuts off the display when the phone is raised to the ear, which relies on infrared, capacitive technology or both. Besides preventing accidental touch commands during a call, it extends battery life, since the screen is always among a handset's most power-hungry parts.

Some phones use more advanced infrared sensing. Apple's Face ID projects a pattern of dots to build a facial depth map and compares it against the map saved during setup, with the primary purpose of replacing passcodes and passwords. On some devices facial recognition is attention-aware, meaning whether the user is looking at the screen can determine brightness, alert volume or whether sensitive content is displayed. Because of the potential for abuse, manufacturers go to considerable lengths to keep facial data from leaving the phone, including heavily encrypted authentication chips.

A phone's NFC chip is another sensor tied to valuable information. It detects a similarly equipped device and transmits data across an extremely short distance, generally an inch or two. That short range is what enables retail payments, digital keys, device pairing and direct file transfers, and it is why only vetted apps are granted access.

Most touchscreens also qualify as proximity sensors. Capacitive screens react to the electricity in the human body, so even the slightest gesture registers, which is the source of many accidental commands; fingers can easily come close enough for the screen to register a touch without a physical tap. Pressure-sensitive screens exist, but anyone who has used them can attest to how cumbersome they are.

Bluetooth occasionally plays a part as well. Using Bluetooth Low Energy, a phone can automatically detect and communicate with nearby devices, such as item trackers or beacons installed for purposes like advertising. There are more benign uses: a beacon at a sports arena might prompt a phone to display a season pass on the lock screen, saving the user a few seconds.

Stretching the definition of proximity further, some phones use LiDAR sensors to map nearby rooms and objects, or to speed up camera focusing in dim conditions by bouncing infrared light off subjects. The focusing role is the main one, since a camera system has difficulty discerning objects when there is barely any contrast to work with.

Turning this hardware off is only partly possible. Bluetooth and facial recognition are simple to disable, and Android phones that support NFC generally offer a toggle in settings under connections. Apple's iPhones do not provide an NFC toggle; the most a user can do is disable features that rely on NFC, such as Bringing Devices Together under Settings, General and AirDrop. LiDAR and the screen shutoff sensor generally cannot be disabled without invoking a special developer mode intended only for highly technical users.

Engadget reports that there is usually plenty to lose and little to gain from disabling proximity technology. A phone with Bluetooth and NFC switched off may be somewhat more secure, but attackers must resort to extreme measures to exploit those systems, which are not directly reachable from the internet and offer little that can be triggered automatically in person. Facial recognition typically makes a phone more secure rather than less, the publication states.