The Sensors That Make the iPhone so Cool

The coolest interface tricks that the iPhone, iPad, and iPod touch can perform — from dimming a phone screen when it's held up to your head to undoing an action by shaking the device and more — are thanks to the sensors built into those devices. Without these sensors, none of the devices would work the ways we know and love.

The Sensors Built Into the iPhone, iPad, and iPod touch

Not every model of the iPhone, iPad, or iPod touch has the exact same set of sensors. The features delivered by the sensors are also based on what operating system version is installed on the device. That said, the most common sensors used on the iPhone and other devices include:

• Proximity sensor: This sensor determines how close the iPhone is to your face. It helps the iPhone turn off its screen automatically when you hold the phone up to your ear for a phone call. This is necessary to prevent accidental button taps on the side of your face when talking. Used on iPhone
• Accelerometer/Motion sensor: This sensor helps the screen automatically switch from landscape to portrait modes and back again based on whether you’re holding the phone vertically or horizontally. Used on iPhone, iPad, and iPod touch
• Ambient Light sensor: This determines how much light is available in the area surrounding the iPhone, iPod touch, and iPad. With that information, the device automatically adjusts its screen brightness to conserve battery life and reduce eye strain. Used on iPhone, iPad, and iPod touch
• Moisture sensor: This sensor isn't visible in the onscreen interface or accessible through the iOS. The moisture (or water) sensor is a little red indicator that appears after the phone has been submerged in water. Depending the model, it can appear in the Dock Connector, Lightning port, or in the headphone jack. If you're buying a used iPhone, check for this indicator to make sure the device doesn't have any water damage. Used on iPhone, iPad, and iPod touch
• Gyroscope: A three-axis gyroscope was included starting with the iPhone 4, the 4th Gen. iPod touch, and the iPad 2. By combining the gyroscope with the accelerometer, this sensor can operate on six axes. This is designed to make the devices more sensitive, responsive, and powerful for gaming, since they can react based on how they're held and moved. Used on iPhone, iPad, and iPod touch
• 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 feature and other location awareness tool to help determine your iPhone's location, which direction it's facing, and to get you where you're going. Used on iPhone
• Barometer: Barometers assess air pressure to help, in part, to determine altitude. This sensor is used for location and directions features. It can help determine the more precise location of your device. Used on iPhone
• Touch ID: A thumbprint sensor embedded in the Home button lets you secure access to your device with your biometric data. It can also be used to authorize purchases and to unlock apps. Used on iPhone, iPad, and iPod touch
• Face ID: Introduced with the iPhone X, Face ID uses a complex system to identify a person's face to provide secure authentication to both the device and to services including Apple Pay. It replaced Touch ID on most models. Used on iPhone and iPad

Other Hardware 'Sensors' in the iPhone

Although they're not generally thought of explicitly as sensors, the cameras and microphones embedded in the iPhone, iPad, and iPod touch devices function like sensors. So are the devices' Wi-Fi chips and cellular radios. That said, most device manufacturers consider their radios and cameras to be separate from sensors when listing them in tech specs and device manuals.

Other types of sensors that are rarely revealed to the user through iOS include thermal sensors. These are used to identify when the device has gotten too hot to safely operate without running the risk of damaging the hardware.