Scientologists use a small device called an "E-meter" to read everything from "undetected thoughts" to your past lives.

They even use the machine as part of marriage counseling.

In her 2011 book Inside Scientology: The Story of America's Most Secretive Religion Janet Reitman talks about the history of the E-meter and what happened if it detected something church leaders didn't like.

The machine works by measuring a person's Galvanic skin response and resistance to electricity. Trained Scientologists allegedly use these measures to determine whether a person has been rid of negative experiences, like memories of a drug addiction, or bad thoughts about the church.

One former Scientologist, Mark Fisher, tells Reitman how the machine was used in the early 80's:

"....The E-meter, now serving as a true "lie detector," proved to be a remarkably efficient, if biased, judge. Almost everyone who went out in front of one of these tribunals, said Fisher, was found guilty and denounced as a traitor."

And what would set the machine off:

"Just a single negative thought about (founder) L. Ron Hubbard, (leader) David Miscavige or anything else that might be viewed as critical of Scientology would be discovered by the e-meter and 'boom, you were denounced and out of there,' Fisher said."

You can buy your very own E-meter on eBay for $2000, although the Wikipedia entry claims church officials only recognize readings by trained Scientologists.