Abstract: Each person underground in the mine carries in his helmet lamp a continuously operating transmitter the signal of which is detected by a receiver. The receiver or the antenna thereof is installed, in one embodiment, in a Faraday cage that surrounds the dangerous area, such as the feed side of the crushing machine or the delivery end of a conveyor. In another embodiment, directional antennas are located at the approaches to a blasting area, for example. In either case, when a signal is detected indicating the presence of a person in the danger zone, in the case of the Faraday cage, or near the danger zone, the conveyor is stopped or a warning is sounded, as the case may be.