While the validity of polygraph tests in court cases is considered
questionable, when it comes to hiring for law enforcement and other
public service agencies, they are used with great frequency -- and
quite legally -- as a screening tool.
It my understanding that the vast majority of Fire Departments and
Police Departments these days use polygraph tests to aid in their
selection of candidates, to avoid problems that have occurred in the
past where "firebugs" (people who get off on starting fires) and
various kinds of people who engage in criminal activities have gotten
positions with fire departments and police departments. These days,
I'm guessing that departments which do NOT do this are extremely rare.
Note the following results, mostly from pages describing the
application process for specific fire and police departments around
"fire department" polygraph (1,950 results)
"police department" polygraph (10,800 results)