The Technion - Israel Institute of Technology in Haifa has developed an engineless, nano-RPV (remote piloted vehicle). The nano-RPVs have numerous applications including firing a swarm of the miniature vehicles into an area contaminated by gas and the nano-RPVs will identify the type of gas.
Once in contact with the gas, the RPVs change colour providing a visual indication of the contaminated area. The tiny RPVs would be carried with the wind along with the gas itself, constantly changing colour and indicating the danger zone of gas. The nano-RPVs could be used for something like a road tanker mishap through to a terrorist attack.