The breathalyser may become obsolete in testing for drunk and drugged drivers. A new device, The Impairment Detector, measures motor behavior instead of testing for particular substances and the British are finding it very successful. It may also become the test of choice to determine if someone is driving under the influence of drugs. From The New Scientist:

Whether you are drunk, drugged, tired or ill, a new device promises to measure whether you are fit to drive. If successful in trials, it could replace the breathalyser, which only measures alcohol levels. The new hand-held device takes a different tack, by assessing motor control, ability to react to the unexpected and concentration

A hand-held device designed to identify drivers impaired by drugs, alcohol or excessive tiredness, is being evaluated by the British police. The device is intended to deliver a quick yes or no verdict on whether a person is in a fit state to drive and works by assessing the driver's behaviour, rather than testing for particular substances. It is the first of its kind to be tested by police anywhere in the world.