An active tag has a power source; a passive tag does not. Active tags use a battery, have a limited life and cost far more. The antenna is a device that uses radio waves to read and/or write data to the tags. The reader manages the interface between antenna and management system. A big advantage of RFID technology over bar-codes is that the tag does not have to be directly in the line of sight of the reader. Tags can be detected by readers remotely because the radio waves can pass through many materials (see, for example, www.ems-rfid.com). Experiments are being conducted across a broad range of frequencies – 125 Khz to 2.45 Ghz for chip-based tags – but standards are still being debated in many sectors. The management system enables data from tags to be collected and sorted for the purposes of management information and action.