Every smartphone has built in hard- or software-sensors. With Sensor Manager you can get a list of the sensors on your device including information like vendor, version, power and resolution. Sensors are used by apps to observe environmental influences affecting your phone. Some game apps use them to calculate the current position relative to the ground or e.g. like the phone app, sensors are used to measure the disntance between your ear and the phone while talking.

With Sensor Manager you can do a live observation of the data coming from the sensors.
Explore the hardware of your smartphone a little bit more!