A polygraph or lie detector is a device that measures and records several physiological responses such as blood pressure, pulse, respiration, breathing rhythms and body temperature while the person is subjected to a series of questions. It is believed that that false answers will produce distinctive measurements on the device.
Season 2[]
When Detectives Dutch Wagenbach and Claudette Wyms were investigating the murder of Leah Madson, they asked the main suspect - Stu Kleinsausser - if he would be willing to take a lie detector test. He refused to, saying that he had heard the tests weren't reliable and there was a chance that he might come up guilty when he wasn't. Later, Dutch argued to Captain David Aceveda that an innocent man would never say that.
Season 4[]
Captain Monica Rawling asked Detectives Shane Vendrell and Army Renta if they would be willing to take a lie detector test to corroborate their involvement in the murder of Angie Stubbs.