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When the governor of Vermont vetoed a marijuana legalization bill this week, he said he was especially worried about stoned driving. He wants to hear more about an “impairment testing mechanism” to detect it.

The problem is that no such mechanism exists. There is no Breathalyzer for pot.

Urine and hair tests can detect whether a person has used marijuana or other drugs within the last few days or weeks, but they can’t tell when a person is stoned at any one moment.

A couple of startups are racing to change that.

Oakland-based Hound Labs and Cannabix Technologies of Vancouver, British Columbia, are developing small handheld devices with tubes that people can blow into, just like the roadside tests that detect drunken drivers.

Hound Labs announced on Tuesday that it has raised $8.1 million from the venture capital company Benchmark, which funded Uber and Tinder, and has started clinical trials in conjunction with the University of California, San Francisco.

The Hound device is designed to detect both marijuana and alcohol in human breath. Dr. Michael Lynn, the CEO, said his company is planning to sell it by the end of the year.

“We tested on so many people now that we’re quite confident,” he told CNNMoney.

He said his company’s device will cost $600 to $800 and will be sold to police departments — and employers, too. In the eight states where recreational pot is legal, companies might not care whether their workers smoked weed the night before, but would definitely care if they are driving trucks or school buses while stoned.

Lynn, an emergency room doctor, said the device uses chemistry to pick up THC molecules in the breath, which are detectable for about two hours.

In Canada, which is moving to legalize recreational marijuana next year, Cannabix Technologies is working on a similar device to detect THC molecules.

Kal Malhi, the company president, hopes to start selling it in about a year and half, for $1,000 to $1,500. Testing began in March.

“We know it works,” said Dr. Bruce Goldberger, a forensic toxicologist and science adviser to the company.

Unlike an alcohol Breathalyzer, which estimates the amount of alcohol in the blood to determine a degree of drunkenness, both pot devices simply give a yes or no on the presence of THC.

Police don’t have a roadside drug testing tool like this. Goldberger said police in other countries sometimes use saliva swabs that can detect drugs, but those haven’t caught on in the United States.

Bob Griffiths, a retired officer and the director of police standards and training for the Alaska Department of Public Safety, said saliva testing technology “has not proven reliable.” This is why it was never adopted in Alaska, where recreational marijuana sales became legal in October.

Griffiths said Alaska police currently conduct field sobriety tests that he described as “fairly rudimentary,” and that the marijuana Breathalyzer “shows promise.” But it still has to be tested by the police, and approved by the courts for use as evidence.

He said the technology is important because it could detect drug impairment in drivers who are not drunk.

“I’ve arrested people who had zero-zero alcohol but they could barely stand up,” he said. “I would say that recreational marijuana, whether legal or not, has always been a problem with impairment with drivers in Alaska.”

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