Soon any adult over the age of 21 will be able to buy marijuana legally in California. And as officials scramble to lay down the rules for this new industry, there’s still something the state is missing — police have no good way to tell when you’re driving under the influence.

That’s the problem Oakland-based Hound Labs is trying to solve. The startup on Tuesday said it raised $8.1 million and began clinical trials for its portable marijuana breathalyzer test — the first of its kind.

[related_articles location=”left” show_article_date=”false” article_type=”automatic-primary-section” curated_ids=””]“In the past, employers and law enforcement professionals focused on possession and use; after legalization, impairment – whether behind the wheel or on the job – becomes the new enforcement paradigm,” Mitch Lasky, a Benchmark partner who invested in Hound Labs’ latest round of funding, wrote in a news release. “Groundbreaking science is necessary to make an accurate measurement of recently used cannabis, and Hound Labs is uniquely positioned to deliver a solution to the market that respects the needs of the enforcement community as well as the rights of legitimate cannabis users.”

With its investment in Hound Labs, Benchmark, a backer of Uber, Twitter and Instagram, joins the slowly growing ranks of investors willing to fund marijuana tech companies.

Fullerton Police Officer Jae Song conducts a field sobriety test on a driver suspected of driving while impaired by marijuana. Officer Lenny Ledbetter assisted on the stop. (Bill Alkofer, Orange County Register/SCNG)

Technology already exists to test for THC — the psychoactive ingredient in marijuana — in users’ blood, saliva and urine. But the chemical can remain in those bodily fluids for days or weeks after smoking or ingesting marijuana, meaning a user risks being wrongfully accused of DUI even if he or she is no longer under the influence of the drug.

When THC instead is measured on a user’s breath, the molecules are detectable for just a few hours before disappearing, according to Hound Labs. The company says its method can detect the chemical after a user has smoked or eaten marijuana.

The Hound device works like an alcohol breathalyzer in that it’s a small, portable device the subject blows into, and it can be used by police during roadside stops, or by employers at work. But unlike an alcohol breathalyzer, which measures alcohol molecules in parts per thousand, Hound’s machine measures THC molecules in a user’s breath in parts per trillion, according to the company.

Hound Labs began clinical trials of the breathalyzer at San Francisco General Hospital earlier this month. In September the company said its product completed successful roadside tests with law enforcement officers.

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