Whether the machine works or doesn't work is irrelevant if they convince you during the poly that it does work. I had one, and the technician was far more intimidating than the machine. If I had something to hide, by the end he would have gotten it out of my I'm sure.
When people are "prepared" for the polygraph (say a mole) they are often trained to construct alternative mental models that would let them answer damaging questions without appearing anxious.
For example, they might organize an obvious seemingly accidental meetup in a some monitored public place (train station) with a foreigner from a specific country so when the question is asked "have you met with foreigners from country X" they can say "yes, I sat next to one when taking the train".
Whether the machine works or doesn't work is irrelevant if they convince you during the poly that it does work. I had one, and the technician was far more intimidating than the machine. If I had something to hide, by the end he would have gotten it out of my I'm sure.
Right, often they are simply used to indicate when a line of questioning is stressing out the subject and to continue on that line.
When people are "prepared" for the polygraph (say a mole) they are often trained to construct alternative mental models that would let them answer damaging questions without appearing anxious.
For example, they might organize an obvious seemingly accidental meetup in a some monitored public place (train station) with a foreigner from a specific country so when the question is asked "have you met with foreigners from country X" they can say "yes, I sat next to one when taking the train".