Aside from bloodshot eyes, constant snacking, and a litany of questions starting with, “You ever notice…,” it’s pretty hard to tell if a stranger is high. You may have your guesses and reasons, but it’s not like there’s a breathalyzer…yet. Yes, it’s coming, says Bloomberg, because as more people drive stoned in states where recreational marijuana is legal, law enforcement officials are realizing they don’t exactly have an effective plan for on-the-go smokers.

That’s why Washington turned to Herb Hill, a professor at Washington State University, who has worked in chemical detection for decades. In fact, Hill’s been keen on building a breathalyzer for drugs since 2009. However, since he’s also on his way to retirement, he brought on his graduate student Jessica Tufariello to help.

HILL: “It’s an interesting project to end on, and an important one. I haven’t seen anybody who has determined how that relates to being impaired.”

To evaluate impairment, the pair decided on a technique called differential mobility spectrometry (DMS). In such a process, two electric fields keep THC ions flowing through a sensor. The first field alternates its charge between positive and negative, and as the second field’s charge counteracts, “the THC makes it through, but the other ions don’t.”

To ensure no false positives — akin to poppy seeds botching drug tests — Tufariello even pretended to be a stoner by mimicking munchies.

TUFARIELLO: “I would go eat at Taco Bell and Thai Ginger and drink lots of coffee to contaminate my breath.”

They were good there, and then the research led to one of the greatest experiments of all time: paying people to get high — or kind of paying people to get high. Due to federal regulations, they couldn’t actually supply the pot, do any of the testing on campus, or even technically say they were paying volunteers to smoke.

TUFARIELLO: “We had to be very clear that we are paying people for their time.”

To circumvent, the smokers would make $10 by calling Tufariello before they were about to get high, who sample their breath. Then she’d test their breath afterward. To keep a tight fit on variables, everyone, at Tufariello’s request, smoked the popular strain known as Blue Dream.

The tests were successful, hitting 81% detection before improving to 89% detection when the team were given new tools by Chemring, the company sponsoring the research. Chemring aims to have a weed breathalyzer prototype for police officers to use in the field by fall.

The high times, they are a-changin’.

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