Abstract: A gaseous detection system for detecting the existence of a certain gas and further the detection of a certain level or percentage of that certain gas within a certain environment. An example is use of the gas detection system in a motor vehicle to aid in determining when a driver of the motor vehicle may be driving under the influence of alcohol, and for providing an appropriate warning signal that may be viewed from the exterior of the motor vehicle. The system includes a sensor unit (214) for sensing ethanol in the atmospheric contents of the motor vehicle's interior, for example, a unit for providing an actuation signal in response to the sensing unit (214), and a signal unit (233) that generates a signal which can be utilized for many purposes, for example, causing at least some of the exterior lights on the motor vehicle to alternately flash on and off in a substantially non-standard pattern.