Mr. Grogan is quick to point out the difference between a traditional polygraph examination, which can take up to two hours, and those shown on television. Viewers are “not seeing the boring, real exam, they’re seeing a re-creation,” he said, with the length of time condensed and participants sometimes encouraged to answer angrily or to behave with particular animation. The real test is slow, there’s more of a pause after the previous answer, and many questions are asked to establish a baseline reading. “We tell all involved that for best results we need to test a person three times,” he said. “Sometimes a filming schedule doesn’t allow that.”

Mr. Grogan knows filming schedules well. He’s been on “Beauty and the Geek,” “Tough Love,” “Flavor of Love,” “Divorce Court” and many, many more.

Some shows have become so adept at polygraph segments that the cameras are not readily apparent in the examination room. Forgetting they are being filmed occasionally leads some participants to offer bribes.

“On some relationship shows, when someone is going to lose their wife and their kids and everything, it’s amazing what they’ll offer to falsify their past,” Mr. Grogan said. “I have people beg me, ‘Please, I know I did wrong, but you have to pass me, or this bad thing will happen.’ ”

Mr. Grogan has some sympathy. Part of his training involved taking polygraph tests as well. “Until you’ve had one, you don’t know the fear and what’s going on through their mind,” he said. “You can hear your own breathing, you feel your heartbeat at your fingertips. We know it’s not an easy thing to go through.”

He has less compassion for those who think they can beat the test. “When you tell a lie, you’re human, deep inside, you know you’re trying to get away with something,” he said. “It makes your nervous system do what it does, and it gets picked up with our equipment.” Some participants have tried to outsmart the machine by inserting a tack in their shoe to alter their readings and thus possibly interfere with the results, a cheating method that Mr. Grogan called an old wives’ tale.