Driving while stoned isn't just stupid, it's also against the law. And in the four states where marijuana has been legalized for recreational use, there's a growing concern that loaded drivers running to 7-11 for another pint of Americone Dream is becoming an issue. Enter the weed-detecting breathalyzer.

Until now, the only way to find out if a driver is high is through a blood test or roadside sobriety test. Blood tests aren't quick (they can take up to 24 hours) and touching your nose and walking a line isn't exactly conclusive.

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Add in the fact that, according to the Washington State Patrol, one-quarter of all blood samples taken from drivers in Washington – which legalized the nation's second favorite smokable two years ago – turned up positive for pot in 2013, and law enforcement is looking for a better way to determine if a driver is stoned when they're pulled over.

That's where researchers from Washington State University come in, developing a handheld breathalyzer to spot THC – the psychoactive component in pot – that's a bit different from its alcohol-detecting counterpart.

WSU chemistry professor Herbert Hill says that the team is using ion-mobility spectrometry – the same tech used by airport security and custom agents to detect drugs and explosives – and repurposing it for the new device.

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Unlike an alcohol breathalyzer, the WSU solution won't determine how stoned a driver is, but instead just detect the presence of THC. After that, police would follow up with a blood test to be used as evidence in court, similar to an alcohol DUI.

The initial prototype for the THC tester should be done before Christmas, with human tests taking place in the first half of 2015. After that, the WSU crew wants to take the device out into the field.