For police officers, pulling over drivers who may be intoxicated is something of a guessing game. Are they swerving between lanes? Are they driving unnecessarily slow or fast? They might be overtired, they may have had too much to drink. An officer won’t know the answer for certain until they pull the driver over and give him or her a sobriety test or use a breathalyzer.
But a new laser detector developed by a team of researchers at the Military University of Technology in Poland might one day remove that guesswork. The device can sniff out high blood-alcohol levels from 20 meters (about 65.5 feet) away by measuring the reflection of a laser beam through a car window.
How it works: A laser emitter and receiver sit on one side of the road, while a mirror sits on the other. As a car passes, the emitter sends a laser beam through the vehicle's window and bounces it off the mirror. The beam is sent at a wavelength that can be absorbed by any alcohol vapor—so, any power loss equates to the presence of booze in the car, researchers say.
“If there is no alcohol, there is no absorption,” Jaroslaw Mlynczak, a researcher on the project, told Smithsonian.com. “The higher [the] concentration of the alcohol inside the car, the lower [the] power we measure, because the beam is absorbed by the alcohol.”
The method is known as standoff detection. Currently, the military uses similar methods to sniff out chemical weapons, hazardous materials, and IEDs. Speed guns also rely on a reflected laser signal, but bounce the light off of passing cars instead of stationary mirrors.
So far, the researchers have only tested the laser in a lab on a stationary vehicle and on private roads on university grounds. In the lab trials, they were able to detect a blood-alcohol level of 0.1 percent. The legal limit in most states is 0.08, but the National Transportation Safety Board has suggested in recent years that states lower it to 0.05.
The laser could change how police are able to monitor our roads, though Mlynczak says the system, still a prototype, requires refinement to increase both its accuracy and the distance at which it can measure alcohol levels.
Another issue researchers will face: working with car windows. The system still needs a better way to compensate for laser power lost not from absorbing alcohol, but from the act of passing through a car’s windows.
The second, and larger, issue is the effect open windows can have on the accuracy of a reading. If "there is air turbulence, and the concentration of alcohol is decreased ... we can’t measure it appropriately,” Mlynczak says.
An intoxicated passenger, not driver, could also trigger the laser.
Though there isn’t a way to work around those shortcomings right now, Mlynczak stressed that his system isn’t meant as a silver bullet—it's “designed to cooperate with a policeman,” not replace one.
In order to pull a driver over, police still need to have reasonable suspicion that a driver may be intoxicated. It’s too soon to tell if Mlynczak’s system will meet that standard. But should a police department wish to implement the system, Mlynczak says, it could be ready for commercialization within a year. Law permitting, of course.