As a mystery writer, it always astounds me when I read a book in which lie detectors are used, or when I hear police departments and federal agencies claiming that someone has either passed or failed a lie detector test, as if the “test” actually has any relationship to the truth.

Now, the McClatchy News Service has reported that a technical glitch in the LX4000, one of the most popular models, might have labeled truthful people as liars or the guilty as innocent.

According to the report, the technical glitch produced errors in the computerized measurements of sweat, supposedly one of the key indicators that someone is either lying or truthful. The problem was first noticed a decade ago but never shared prior to the McClatchy story.

Over the years, scientists have repeatedly questioned the validity of polygraphs and their reported ability to accurately identify liars. Most U.S. courts do not allow information obtained from lie detectors to be submitted as evidence, which should tell you something about the “accuracy” of the machines.

Still, fifteen federal agencies and many police departments across the country rely on polygraph testing to make hiring and firing decisions. Detectives and prosecutors often rule out criminal suspects who pass and focus on those who don’t. That an innocent person suspected of a crime today should be asked by police to take a “lie detector test” to determine if they are being truthful is akin to using phrenology to measure intelligence.

So my advice to aspiring mystery writers is to avoid any reference to these machines, except if you intend to disparage them.