For another device like a smartphone to use any of the Bluetooth "services" which the micro:bit has, it must first be [paired with the micro:bit](/reference/bluetooth/bluetooth-pairing). Once paired, the other device may connect to the micro:bit and exchange data relating to many of the micro:bit's features.
The Bluetooth accelerometer service allows another device such as a smartphone to wirelessly receive data from the micro:bit's accelerometer. An accelerometer detects motion. More precisely, it measures acceleration in one or more of three directions which we call X, Y and Z.
Using the Bluetooth accelerometer service you could, for example, create a smartphone application which makes a loud noise whenever your micro:bit (or the important thing you've attached it to) is moved. Or you could use your micro:bit to control the movement of a cartoon character in a game on your smartphone just by tilting the micro:bit in the direction you want the character to move in.
No additional code is needed on the micro:bit to use the Bluetooth accelerometer service from another device.
For more advanced information on the micro:bit Bluetooth accelerometer service including information on using a smartphone, see the [Lancaster University micro:bit runtime technical documentation](http://lancaster-university.github.io/microbit-docs/ble/accelerometer-service/)
