Abstract: An apparatus placed at the "fenceline" (perimeter) of a site, to detect the possible existence of contaminants within the air and transmit an audio signal to a remote location indicating an irregularity in the air quality. Conventional audio transmitters such as a walkie-talkie may be used to detect an audio alarm signal from the contamination detection device and be received by a receiver, such as another walkie-talkie at a remote location. The monitoring system may be housed in a portable enclosure to protect the equipment from weather, vandalism or theft.