radio receivers
Radio receivers receive wireless signals from a radio transmitter. If the wireless transmitter code is allowed in the radio receiver, the radio receiver will enable its output (typically a Form C relay). Radio receivers work in the unlicensed bands of the frequency spectrum (300MHz, 315 MHz, etc).
Radio receiver / radio transmitters are convenient for the opening and closing of gates as the parker has control of the gate from within their vehicle wirelessly. Ranges vary.