An apparatus comprises: a memory to store sensor data and at least one processing core that compiles a message based on the sensor data； the message is transmitted from the apparatus, causing receiving in the apparatus of a machine readable instruction； and estimated activity type is derived using the machine readable instruction. The sensor data is preferably acceleration sensor data； additional sensor data may include sound or vibration data. In use the apparatus derives a user activity and may receive a message from a user device. Methods for detecting activity type are also disclosed including the steps of storing sensor data 510, compiling a message 520, transmitting a message 530, receiving an instruction 540 and deriving an activity type 550. The apparatus and methods are preferably used to detect a sporting or physical activity performed by a user wearing a user device which communicates with a server or back end apparatus.
