Two Tiny iPhone Sensors

Look really closely at the top of your iPhone where you can find two hidden sensors. The sensor on the right is a Proximity Sensor. It'll detect when objects are extremely close to it like your face during a call or your jeans while in your pocket. When it does, your iPhone's screen and its touch functions turn off.

The sensor on the left is an Ambient Light Sensor. This is for your iPhone's auto brightness setting. It measures the brightness of the environment around you, then it optimally ses your screen's brightness.