In order to control the events in the game and potentially control an avatar, input from so-called user input devices is used. For a desktop computer, this would be the keyboard and mouse in most cases, and a controller for consoles. For most devices that AndEngine will run on, we are likely limited to a touchscreen, and in most cases, sensors such as a motion sensor.
The Android Compatibility Definition Document (CDD) defines which sensors are required or optional for a device to be certified as Android compatible. It can be found at http://source.android.com/compatibility/. For the current (at the time of writing this book) version of the CDD, all sensor types are optional. This, sadly, includes the motion sensor. The CDD, however, does list the following sensors as types that the device should (not "must") have:
Accelerometer (motion sensor)
Magnetometer
GPS
Gyroscope
Barometer
Out of this list of sensors, exactly none are guaranteed to be present, but some (or all) can be present....