1. Proximity sensor:  This sensor determines how close the device is to your face. It helps to turn off its screen automatically whenever you hold the phone up to your ear for a phone call to prevent accidental button taps. 

2. Accelerometer/Motion sensor:  This sensor enables the smartphone’s screen to automatically switch from landscape to portrait modes and back again based on whether you’re holding the phone vertically or horizontally.

3. 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 is designed to make the devices more sensitive, responsive and powerful for gaming, allowing them to react based on how the devices are held and moved.

4. Ambient Light sensor:  This determines how much light is available in the area surrounding the smartphone and automatically adjusts the brightness of the screen in order to conserve battery life and to calibrate the screen to ease eye strain.

5. Compass:  This sensor is used with the device's GPS and other location awareness features to help determine your smartphone's location, which direction it's facing, and to get you where you're going.

6. 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.

7. 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.

8. 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.