This equipment is designed to support the topic of the Electromagnetic Spectrum so that a practical demonstration of the application of infra-red radiation can be given. The complete system consists of a transmitter and receiver unit with built-in battery power. The transmitter unit has the electronics for producing a modulated infra-red beam and is contained in a small plastic enclosure measuring just 100 x 60 x 22mm. The modulation frequency is user adjustable in the audio range. The receiver has the detector and amplifier with integral loudspeaker with built-in gain control to adjust the sensitivity. Typical range is up to 2m with the tone disappearing if any obstruction passes through the beam.