Abstract: A system of detaining a robber on the premises robbed after the robbery has taken place. The premises is provided with lobby entrances having inner and outer doors through which persons entering and leaving the premises must pass. Once a robbery commences, the doors to the lobbies are automatically locked. In the money handed to the robber, there is concealed a radio transmitter which transmits a narrow wave length signal. Mounted in the wall adjacent to each lobby inner door inside the premises proper there is mounted a receiver which is tuned to the narrow wave length and which has a limited range of reception on the order of about five feet or so. When the transmitter carried by the robber is within the receiving range of the receiver, the inner lobby door can be opened from inside the premises. Once the robber enters the lobby, neither of the lobby doors can be opened by the robber and he will be caught in the lobby.