A sensor tag which in use will be affixed to a vehicle for obtaining vehicle telematics data includes a battery for powering the tag and a processor running executable code to process accelerometer data. An accelerometer measures the acceleration of the tag and thereby of the vehicle, and also controls the operation of the processor. A memory is used for storing a unique tag identifier of the tag and for storing trip data including information about trips and acceleration data. Finally, a communication module is used for short range wireless communication with a mobile communications device located in the vehicle via a short range wireless communications protocol, the communication module transmitting the tag's unique identifier and a sequence of time stamped acceleration data. The mobile communications device obtains GPS data, combines this with the acceleration date and transmits this to a server for analysis.