Last week, we learned that since 2012, yet another piece of battlefield technology has been used by police agencies across the country.

"At least 50 U.S. law enforcement agencies have secretly equipped their officers with radar devices that allow them to effectively peer through the walls of houses to see whether anyone is inside," USA Today reports. "[A]gencies, including the FBI and the U.S. Marshals Service, began deploying the radar systems more than two years ago with little notice to the courts and no public disclosure of when or how they would be used."

Effectively powerful motion detectors, the handheld radars can locate the slightest movement from up to 50 feet away. And their use has exposed troubling privacy concerns reminiscent of other police overreaches.

The potential for abuse: The technology is meant to help protect police when they enter a building – if they have a search warrant in hand. The trouble is that some officers have not been bothering with such formalities. The radars' use only came to light after a parole violator was arrested thanks in part to police using the devices to confirm his location in a building. A federal appeals court ultimately upheld the search on other grounds, but worried about the warrantless use of the devices.

As USA Today notes, the Supreme Court has already restricted snooping methods outside houses. In 2001, SCOTUS found that the Constitution protects people from having their homes scanned with thermal imaging technology without a search warrant. Then in 2013, the court limited the use of notoriously unreliable drug-sniffing dogs outside of our homes.

Law enforcement officials argue that the radars are crucial to officers' safety in extraordinary, dangerous circumstances. But as happens all too often, the extraordinary quickly becomes dangerously ordinary. After all, SWAT teams were originally intended only to handle extreme situations — violent riots, hostage situations and the like.

In 1980, there were only 3,000 SWAT raids in the U.S., according to criminologist Peter Kraska of Eastern Kentucky University. The wars on drugs and terror, however, have helped ensure a swift redefinition of "extreme." Now there are 50,000 SWAT raids every year.

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Part of a larger pattern of surveillance: What we can learn from the radar use, the increase in SWAT raids and other broader policies like the Patriot Act is that when not rigorously restricted by legislatures and courts, these measures tend to metastasize in unpredictable and often frightening ways.

Not just our emails, but our lives in the real world are now open to wanton intrusion, with radars scanning our homes comprising just a small part of a broader trend towards comprehensive surveillance. It's therefore unsurprising that, according the Wall Street Journal, the Drug Enforcement Agency and the Justice Department have been using license-plate readers to track all the movements of vehicles within the U.S.

The erosion of privacy is not something that only dangerous criminals should worry about. Whether you realize it or not, you're probably a criminal too. Attorney Harvey Silverglate argues in Three Felonies a Day: How the Feds Target the Innocent that the proliferation of vaguely worded criminal laws has virtually guaranteed that the average citizen commits all sorts of abstruse crimes pretty much all the time. You could go to jail if you throw away junk mail addressed to the wrong house, for instance.

Police might not arrest to you for every petty offense. But they can. There's nothing stopping overzealous police from busting every jaywalker (which many cash-strapped departments have actually been doing) or from construing your Facebook posts as "terroristic threats." Overzealous police, incidentally, also make life-shattering mistakes. Now imagine the police scouring your entire life or following your every move. It's not obvious that you can't be found guilty of something.

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Not all or even most police are bad people looking to get us any chance they get. They don't have to be. Paeans to their service aside, law enforcement agents are not more than human. They are as mendacious, capricious and jealous as the rest of us. And we have given these fallible people tremendous authority to catch every bad guy, to stop every terror attack, with innocent people inevitably snared in the too-wide net.

The importance of protecting our privacy: Strict protections for our privacy can help to minimize the chances that even the most well-intentioned police can abuse their power. As Hanni Fakhoury, a lawyer for the Electronic Frontier Foundation, told USA Today, "The problem isn't that the police have this [radar technology]. The issue isn't the technology; the issue is always about how you use it and what the safeguards are."

It remains to be seen if the courts will restrict the warrantless use of radars in the same way that the Supreme Court restricted police from searching cellphones without a warrant. In that case, the court unanimously found that the right to privacy of our cellphones trumps police convenience. That logic should extend to the privacy of our own homes and our movements as well.