When I was quite young, Dad demonstrated his high-tech polygraph machine on me for the first time and it astounded me (and scared me a little).
It consisted of a length of black thread, ~12", threaded onto a sewing needle (dutifully supplied by Mom).
I was told to lay my left hand on the table (parallel to the frontal plane of my body) and suspend the needle and thread with my right thumb and index finger a couple of inches above the fingers of my left hand. Then I was told to try very hard to *not *swing the needle.
Dad explained that after asking me a question, the needle would slowly begin to swing in one direction or the other and that the direction of the swing would determine the correct response to the “yes” / “no” questions asked. If the needle swung along the long axis of my fingers, the answer was “yes”; if it swung perpendicular, the answer was, “no.” I was wary, but game to try this lie detector thing.
It turns out, I should have retained a lawyer first. Incredibly, the “device” was 100% accurate and it was quickly used as a tool against me.
Dad: "Is your name, “Tibby?”; [needle swings “yes”]; “Are you a monkey?”; [needle swings “no”]; "Do you have a dog named, Pookie?" [needle swings “yes”]; “Did you spill a can of paint on the basement floor?” […needle swings…“yes”]; AH HA! Caught you!
I tried this technique on my daughters when they were young. They just poked me with the needle.