A transponder is a device that emits a signal or responds to a signal sent from another device. Synonyms for transponder include responder, transceiver, beacon, and radio beacon. A responder is a device that automatically responds to a signal from another device. A transceiver is a device that can both transmit and receive signals. A beacon is a device that emits a signal to help guide or locate an object or person. A radio beacon is a specific type of beacon that uses radio waves to transmit its signal. These synonyms can be used interchangeably depending on the context and the specific function of the device.