Abstract: In a system for monitoring and collecting data on the viewing habits of television viewers or radio listeners, to enable operators of networks or television stations, programmers and advertisers to determine the numbers of viewers watching particular programs, a portable personal data collection device comprises a detector for providing a station identifier identifying the particular broadcast signal being received by the receiver, a clock for providing a signal representing time, a memory for storing data, a cellular telephone module for communicating with a central location, a control for the cellular telephone module, and a microprocessor. The microprocessor stores in the memory data comprising the station identification, and the time at the beginning and end of receiving signals from that station. The control is arranged to control operation of the cellular telephone module to transmit the stored data to the central location.