Abstract: In an emergency call system for vehicles on public roads, in which the vehicle is provided with a radio transmitter adapted to selectively emit a signal in a plurality of modes, a testing system having a receiver for the emitter signal, and an attenuator for suppressing and blocking spurious and unwanted interfering noise connected to the input of the receiver. The output of the receiver is fed to at least one filter by which the mode of the signal is determined. The output of the filter is connected to the input of a plurality of switching circuits adapted to operate signal lamps corresponding to the transmitted signal mode.