It used to be that the only way you could get a speeding ticket was if a police officer personally witnessed your overly-fast driving. Then photo radar came along. Well, when it comes to drunk driving, lasers could soon be the equivalent of photo radar. Polish researchers at the Military University of Technology in Warsaw have demonstrated how the high-intensity beams of light can be used to detect the presence of alcohol – even exhaled alcohol – in passing vehicles.

The scientists used a type of stand-off detection, the general term for the ability to identify substances at a distance. Typically, it's used to detect things such as explosives or other hazardous materials, without getting dangerously close to them.

In this particular case, a laser was shone through a car's cabin via its windows, onto a mirror located on the other side of the car, and then reflected back through the windows to a photodetector. Inside the car, alcohol vapor was emitted into the air, in a concentration similar to what would be exhaled by someone with a blood alcohol level of 0.1 percent.

By analyzing the reflected laser light, it was possible to determine how much of the original beam had been absorbed by alcohol vapor in the vehicle's cabin. This in turn allowed the scientists to accurately deduce the amount of alcohol in the air.

The idea is that from there, an automated system could snap a photo of the car showing its license plate number, which would then be transmitted to police waiting down the road. Officers could then pull the car over and subject the driver to a breathalyzer test. The system could not simply issue a ticket based on the laser reading, as the alcohol vapor could be coming only from passengers in the car, or from spilled alcohol.

It's definitely possible that drunk drivers could thwart the system by keeping their windows rolled down to air out the cabin, or by placing laser-blocking items on the window glass. In those cases, however, the system could still alert officers to the fact that those vehicles might be ones to check out.

The scientists are now in the process of optimizing the technology for commercialization by making it more compact, robust and user-friendly.

A paper on their research was recently published in the Journal of Applied Remote Sensing.