An apparatus is disclosed that provides back light for liquid crystal displays. The flow-meter is an electromagnetic flow-meter, also electrically supplied by the supply source of the pump. One or more frequencies in the detection range of the femto cell access point can be jammed, an attachment attempt emitted from the device in response to jamming the frequencies can be detected, and a telephone number of the device can be identified based, at least, on detecting the attachment attempt from the device.