The Sensors That Make the iPhone So Cool

iPhone sensors
image credit: John Holcroft/Ikon Images/Getty Images

At least five sensors built into most models of the iPhone, iPad and iPod touch allow them to perform some of their coolest interface tricks. Without these sensors, none of the devices would be what we know them as today.

The specific provisioning of sensors and their relative capability varies by device type and generation.

The sensors are:

  • Proximity sensor—This sensor can determine how close the iPhone is to your face. This sensor is what helps the iPhone turn off its screen automatically whenever you hold the phone up to your ear for a phone call. This feature is necessary to prevent accidental button clicks on the side of your head when talking. 
  • Motion sensor/accelerometer—This sensor enables the iPod touch, iPad, or iPhone’s screen to automatically switch from landscape to portrait modes and back again based on whether you’re holding the phone up and down or sideways. This sensor is also present on the iPad.
  • Ambient Light sensor—This sensor can determine how much light is available in the area surrounding the iPhone, iPod touch, and iPad and automatically adjust the brightness of the screen in order to conserve battery life.
  • Moisture sensor—The devices also contain a hardware-specific sensor, though this one isn’t related to the interface and accessible through iOS. The water sensor is a little red tab that appears in the dock connector after the phone has been submerged in water. It can also appear as a red dot in the headphone jack. If you're buying a used iPhone, it's a good idea to check for this indicator to make sure the device hasn't been damaged by water.
  • Gyroscope—Starting with the iPhone 4, 4th gen. iPod touch, and iPad 2 there's another sensor: a three-axis gyroscope. When combining the gyroscope with the accelerometer, this combo gives these devices six axes on which it can operate. This capability is designed to make them more sensitive, responsive and powerful for gaming.
  • Compass—All iPhone models starting with the iPhone 3GS also have a compass built into them. This sensor is used with the device's GPS and other location awareness features to help determine your iPhone's location, which direction it's facing, and how to get you where you're going.
  • Barometer—Barometers assess air pressure to help, in part, to determine altitude.
  • Touch ID—A thumbprint sensor embedded with the Home button allows for biometric access to the device and application-level security.
  • Face ID—New with the iPhone X, Face ID uses a 3D camera to identify a person's face to provide secure authentication to both the device and to services including Apple Pay.

Other "Sensors"

Although they're not generally listed explicitly as sensors, the cameras and microphones embedded in the iPhone and iPad devices are, functionally, sensors, as are the Wi-Fi and cellular radios within the devices. Most device manufacturers consider their radios and cameras to be separate from sensors in their tech specs and device manuals.

The hardware itself contains special sensors rarely exposed to the user through iOS, including thermal sensors that identify when the device exceeds its operating tolerances.