The utility of "lie detectors", which I personally imagine most law enforcement people understand, is as a tool of coercion and deception. It's not so much that they believe the devices actually function how they are claimed to, but that it gives the officers some 'legitimate' excuse to prosecute people based upon the intuition of the officer. It's not an accident that all of these systems require a human being to look at whatever readings are taken and "interpret" them. Any real system would include no such feature at all, because putting a human in the loop does nothing but invalidate whatever determination is made by opening up the inevitability of human error. At the end of the day, the verdict of a lie detector is nothing more than "the examiner has a gut hunch the person is lying/telling the truth" + a little bit of extra credibility in the eyes of the uneducated.