The test administrator instructs the subject to follow a point of light that moves across a horizontal plane. The administrator sees an image of the eye in monochrome. Intoxicants break down a person's ability to smoothly track an object, producing a jerking movement, called nystagmus, in the horizontal plane. Nystagmus typically occurs in response to central nervous system depressants. Another measurement involves watching the eye at the periphery of vision.
Alcohol tends to produce large-amplitude tremors that persist for at least four seconds.
If the instrument indicates the possibility of intoxication, urinalysis is used to verify the suspicion. This saves the expense of performing a urinalysis on every employee. Although he didn't want to give precise dollar figures, Campesi said that the device had reduced his cost of testing employees by 75 percent. Another benefit of SafetyScope is that the result is specific to the individual. Campesi said he can run the SafetyScope 24 hours a day, and the results are instantaneous.