Answer:
It is a device for monitoring air quality, typically within a building, to warn against the build-up of explosive gases such as propane, methane, or gasoline vapor. These devices are commonly used in manufacturing facilities using highly volatile solvents (eg for degreasing) or storage facilities for such chemicals.
Inexpensive, single-gas alarms (eg for propane) are avail for approximately $50 for recreational vehicles, to guard against a tank or line leak. Industrial grade monitors which provide telemetry back to a SCADA system will be many times that price.