What police know, and share in public court, routinely sends people to prison.

But, in at least one Florida case, it is what police want to keep secret that kept one criminal out of prison.

The Washington Post tells us the story of Tadrae McKenzie , a Tallahassee teen who used a BB gun to rob a marijuana dealer of $130 worth of street product.

A BB gun is considered a deadly weapon under Florida law and McKenzie faced a minimum sentence of 4 years in prison.

McKenzie's appointed lawyers, however, were able to figure out Tallahassee police were using a "secret" device to track McKenzie's location. A state judge ordered police to show the device — a cell-tower simulator sometimes called a StingRay — to the attorneys.

Instead of showing the device in public court, prosecutors offered a plea "deal of the century" -- six months probation.

What does a StingRay do?

It is a $100,000 suitcase-sized electronic device that tricks all cellular devices in the area into sending data, which can be captured and recorded. The company that makes them, Harris Corp. of Melbourne, Fla., which may have misled the FCC about their use , says the devices are for emergencies only, but untold police departments routinely use them.

Phones don't need to be actively in use to send data to a StingRay, and the devices often interrupt phone service in the area they are used.

Other devices that use cellular networks -- laptops and tablets -- are also tricked into transmitting data.

The ACLU says Tallahassee police have used the StingRay hundreds of times, and not for emergencies.

According to the ACLU, police in 48 states use StingRays, including Georgia .

Judges have to sign off before a StingRay can be legally used, but judges often have no idea what they are signing, according to some reports.

In Washington, police never bothered to tell judges they were using StingRay devices to track phones when asking for permission.

But they got the judges signatures anyway -- 170 times.

That's the funny thing about laws: those who enforce them don't always follow them.

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