Lie detectors LIE. They measure small body changes, supposedly to find a baseline for a true statement, and a change, indicating a lie. At best, they may measure a change, that can be for many reasons. They can be most useful to law enforcement. Telling a defendant that his/her test was guilty can force an innocent person to take a plea of reduced charges. (Police ARE allowed to lie.)
As a result of my torture trauma past, I will never take a chance over it. The environment of being questioned is would be a huge trigger, as I careen in trying to simply getting through a questioning without a full fight or flight meltdown. I consider myself to have a high probability of being a false positive. I have never needed to test it out, fortunately. Courts do not recognize them as reliable, either, but lawyers will use a good result to clear a client, though. Sociopaths, by their lack of conscience, can fool these tests, too.
Brain wave tests supposedly work better, but that is just researchers reports. AFAIK, no rigorous meta studies have been done.