YouTube: How do breathalyzers work? And will there ever be a breathalyzer for marijuana? As pot has become legal in several states, law enforcement has sought a method to detect marijuana use in drivers. This is complicated, though. Breathalyzers for alcohol work on principles that don't necessarily work for pot. And they've been extensively researched, which is difficult to do with federal controls on marijuana. There may never be a breathalyzer for pot, but one thing's is for sure: eating your own feces won't beat a breathalyzer.