Abstract: A training aid (10) for such side arms as revolvers and pistols that comprises a transmitter (18) in the form of a replaceable cylinder (14, when the weapon is a revolver) or of a replaceable insert (114, when the weapon is a pistol or similar piece) and a receiver (16), whereby the transmitter has a release (22) that is activated by the impact of the weapon's hammer (20) and causes the transmitter to emit simultaneously with the impact a brief and narrowly collimated beam (24) of infrared light, the receiver is positioned at a desired distance away and produces a signal when it receives the beam, the beam of infrared light is generated by a diode (66) accomodated in a tube, and the release is at one end of the tube and a device (68, 70, or 168) that focuses the beam is at the other end.