(NPR) The alcohol Breathalyzer came to life slowly, over the course of decades.
From the 1930s through the 1960s, scientists, lawmakers, police and the public quarreled over the veracity of the numbers spit out by the device, the appropriate legal limit for drivers and whether they could trust a machine over a cop's testimony.
Today, the same debate is playing out over cannabis.
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As 33 states and the District of Columbia have legalized pot in some form, Breathalyzer-type devices that could theoretically aid police enforcement have begun appearing in various stages of development. But legal experts and scientists say there's a long way to go before those devices can actually detect a driver's impairment.