A computer-implemented method of triggering an action based on behaviour of a user consuming content at a user device, the method comprising receiving content change signals at a processor executing a content change detection algorithm, wherein the content change signals denote a change of content on the user device; wherein the detection algorithm compares the content change signals with a content change behaviour associated with that device to detect a surfing condition and generates a triggering control signal for triggering an action when the surfing condition for that device is detected.