Abstract: A system for delivering audio advertising messages to shopping carts moving through a plurality of spatially defined transmission zones arranged in the aisles of a store. In the illustrative embodiment, a plurality of transmitters of compact construction are each attached to a shelf within the store. Each shelf transmitter has a spatially defined transmission zone of selected geometry and predetermined dimensions so as to occupy an assigned region of space within one of the aisles in the store. When any one of these transmitters detects a shopping cart residing in its spatially defined transmission zone, the transmitter transmits over its spatially defined transmission zone, a modulated signal carrying an audio message provided by a playback mechanism within the transmitter. A receiver on the detected shopping cart demodulates the received modulated carrier signal and produces an audible signal of the audio message provided by the playback mechanism in the transmitter.

Abstract: A cordless telephone system in which a communications path is established and maintained between a base and a remote unit with the transmission of a binary coded pulse train. Maintenance of the communications path in this manner does not require multiple carrier signals and avoids interference between adjacent remote units. A microphone switch is also provided that prevents accidental turn-on of the remote unit, thus preventing accidental battery depletion.