How much existing advertising technology works seems to be questionable. Lie detectors aren't admissable in court for good reason, but they are still considered useful to help lead investigators in the right direction, especially against people that aren't trained or trying to defeat them.
Mostly because of the placebo effect ie most people think lie detectors work and it makes you uncomfortable and stressed to have a device strapped to you while someone with authority asks serious questions.
It leads them down random directions because false positives are extremely common and more importanty false negatives can lead an investigation away from the truth.
It picks up one set of signals that can be altered based on the interviewer. And is colored by the person trying to understand the test.
