No blood test. No breathalyzer. No getting busted by the cops for DUI.

That's what a new app called MyCanary can help cannabis consumers avoid by letting them check their own impairment levels. This could encourage individuals to wait a few hours before getting behind the wheel if they've toked up, avoiding a costly DUI.

Marijuana is now fully legal for adults in four states and Washington, D.C. Decriminalization is working here in Philadelphia and dozens of other municipalities. The plant is far safer than alcohol. Tens of millions of Americans smoke it every day. Studies have shown that cannabis does not have nearly the same impact as booze when it comes to driving. Nevertheless, some states have some downright draconian DUI laws when it comes to THC. Pennsylvania is one of them.

Any detectable amount of THC in the blood, regardless of actual impairment, can result in serious trouble for a driver in the Keystone State. Just ask a couple Pittsburgh Steelers running backs. Technically, the Pennsylvania threshold is 1 nanogram per milliliter of THC in the blood. That could be present days after a toke.

The National Organization for the Reform of Marijuana Laws is backing the new technology.

Philly420 spoke with the developers to see how it works.

Marc Silverman, who worked on the technical side of the app, said more than 10,000 people have downloaded MyCanary since it was launched in July.

"We hope that this private tool will help individuals consume responsibly and perform safely," said Silverman.

The app uses four games that test things like balance and memory skills. Akin to a fitness app, it tunes into an individual's patterns.

Paul Armentano is NORML's deputy director and has written extensively about DUI laws and the science of cannabis. He consulted on the app's development.

"Unlike field sobriety tests, which have not been validated to identify subjects under the influence of any substance other than alcohol," said Armentano, "the performance tasks provided by the MyCanary app are those that have been identified in the peer-reviewed literature as validated measurements for distinguishing subjects who may be under the influence of cannabis from those who are not."

Armentano said that the MyCanary games draw on the best science about how to measure marijuana impairment.

When it comes to cannabis on the roads, consumers are not always punished for being too stoned to drive but instead simply for trace amounts of weed.

"To be clear, every state criminally prohibits driving under the influence of a controlled substance, including marijuana. In most of these states, prosecutors must provide objective evidence that the defendant recently ingested a controlled substance, such as marijuana, and that the subject was impaired by their recent ingestion to the extent they presented a legitimate traffic safety risk," Armentano said.

"However, in a handful of states — such as Arizona and Pennsylvania — the traffic safety laws have been amended so that the state no longer must provide evidence of psycho-motor impairment. Rather, the state must only show that trace levels of THC or its inert metabolite are present in the driver's blood or urine. Such per se or zero-tolerant laws are an unscientific and disproportionate response to behavior that is already sufficiently addressed by present traffic safety laws, and they risk inappropriately convicting unimpaired subjects of traffic safety violations for engaging in behavior that does not pose any actionable traffic safety threat."

Silverman says that driving is just one of the things MyCanary can help consumers avoid if they have ingested a bit too much.

"Any task - like operating a table saw - that requires intact cognitive and motor skills is a candidate for MyCanary prior to engaging. We want to encourage and support personal responsibility."

Most legal consumers have smoked underground market marijuana for years. But the hush-hush nature of prohibition hasn't helped them understand the physiology behind getting high.

"Consumers require better education in regard to cannabis's potential impact on motor safety and better tools to self-assess their performance," said NORML's Armentano.

One of the big sticking points of legalizing marijuana has been traffic safety. Data has not shown any general negative impact in Colorado or Washington as a result of legal weed. Still, authorities and the public in general may move faster towards regulated cannabis in more states if there is some reliable method to gauge impairment.

Right now police officers look for red eyes and use their noses. Not very reliable. Also, as a society, we do allow a certain level of alcohol behind the wheel, just not too much. Cannabis consumers should have the same consideration.

"Law enforcement requires additional, and scientifically validated, tools to be able to more accurately identify those drivers who may present a traffic safety risk because of cannabis-induced impairment," Armentano said. "The advent of such technology, coupled with greater education and accountability among the cannabis industry and consumers, will both increase public safety while simultaneously increasing public support."

Most people who choose to smoke or eat marijuana for medication, recreation or spiritual use are hard-working members of our communities. They have families, jobs and contribute, positively, to every city and state. So the new app actually puts stoners in charge of looking after themselves.

"It's very interesting and satisfying to see the large number of downloads," Silverman said. "To me, that demonstrates that people want to be responsible and will accept tools that help them accomplish that goal."

Chris Goldstein is associate editor of Freedom Leaf magazine and co-chair of PhillyNorml. Contact him at chris@freedomisgreen.com.