A personal identification device for use with a mobile telephone in a wireless communications network includes an connector mated to a connector of the mobile telephone normally used for a hands-free kit or a data port. In a typical application, a user of the mobile telephone calls a server. The server sends a first telephone signal to the personal identification device. The device responds with a second telephone signal, designed to simulate voice or data activity, depending on the type of connector that is used. The simulated voice activity is structured in such a way as to cause the radio signal transmitted by the mobile telephone to go on and off in response to the simulated voice activity. A nearby receiver can detect the on/off pattern. The on/off pattern is designed to convey a unique identification code.