Abstract: Warning apparatus comprising a transmitter for producing a coded signal and a monitor for detecting such signal; the transmitter including a detection circuit comprising sensors responsive to abnormal conditions at a location in a region near the transmitter, a circuit for generating a coded signal in response to the abnormal condition detected, and a circuit for transmitting the coded signal for reception by the monitor; the monitor including a circuit for receiving the coded signal transmitted, an electronic circuit for decoding the coded signal received, and an electronic circuit for displaying the type of abnormal condition detected by the sensor and the location of the transmitter which detected the abnormal condition.