A new breathalyzer can detect both alcohol and THC. It’s developed by California-based Hound Labs and can detect marijuana use over the previous two hours. It’s an improvement from other tests for potential impairment, which often can tell if the marijuana was used recently or days ago. There’s still no unified legal standard as to how much THC makes someone impaired behind the wheel. A handful of police departments are planning to start testing the device later this year.