The TPA is an active transponder, which was developed for use together with the locator TAL 700.
Upon entering the transmission range of a locator the transponder is woken by a coded 125 kHz signal, which also carries information about the location of the locator. Once woken by the TAL 700 the transponder responds with its ID and the location code it received.
The wake-up range in conjunction with the TAL 700 is as much as 7 m. The low-frequency wake-up field facilitates use behind a vehicle windscreen shielded against UV rays, for example with V-Kool™. It is also possible to detect the transponder inside of the vehicle.