An instant drug swab previously used in jail to detect if prisoners had been using cannabis is being taken to the street to crack down on driving "high" by the Los Angeles Police Department.

The swabs, which use saliva to determine the drugs in a person's system, will reportedly be used during routine traffic stops, and can determine the presence of up to seven different intoxicants.

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While residents may believe they have to submit to roadside testing, one L.A. County criminal defense attorney claims that it might not be smart to do so. His claim: a California court precedent holds that a warrant is needed for a blood test--the same should hold for a saliva swab.

That said, if we look at drunk driving cases as a measuring stick, refusing a roadside test might not be the best course of action. Refusing an alcohol breathalyzer roadside can get you an automatic, one-year suspension of your drivers license.

The tricky thing is that when it comes to cannabis, there is no legal threshold in California that triggers a DUI. And as anyone who has had to submit to drug test knows, THC can stay in your system for weeks. The possibility exists of driving completely sober, having consumed a cannabis product legally days previous to you getting pulled over--and still you could test positive.

So what's the safe move? Obviously, it's a personal call. Marijuana activists seem to be leaning towards refusing the swab, as it weakens a case against the user with lack of roadside evidence.  What seems sure is that until the California legislature addresses what constitutes an illegal THC limit, this will remain a hot button issue.