The polygraph machine is supposed to detect when its subject is lying. The fact that it can't is well-known and well-documented; all a polygraph machine detects are common signs of nervousness. The machine can easily be tricked by many methods, which are available to anyone willing to search for them, and yet the device is still given weight by the system.
Government employees are sometimes required to undergo polygraph testing, despite its inefficacy. Some companies make employment decisions based on mandatory polygraph testing. And a man was recently jailed for passing on common knowledge about the device's flaws.
When accurate and effective lie detection devices are invented, their official use should be embraced, but don't endorse a device less effective than a coinflip.