A beacon device is disclosed for transmitting a proximity indication signal. When a mobile terminal is in proximity to the beacon device the mobile device receives the proximity indication signal and transmits a signal indicative thereof to the network with which it is registered in order to receive discounted calls because it is deemed to be within a special zone (such as the house of the user of the mobile terminal. The device is able to detect movement of device and to inhibit generation of the proximity indication signal to the mobile terminal when movement is detected. In order to detect movement, the device includes means for recording the pattern of selected ambient radio signals to derive a typical value range, means for measuring the ambient radio signals to produce a measurement value, means for comparing the measurement value with the value range to determine whether the device has been moved, and means for selectively enabling transmission of a proximity indication signal to the mobile terminal in dependence upon the determination of the comparing means.