Scanner hobbyist Rick Hansen holds his scanner/Ham radio device at his home Saturday, Nov. 19, 2011, in Silver Spring, Md. In an effort to restrict access to their internal communications police departments around the nation are moving to encrypt them. (AP Photo/Carolyn Kaster)

(AP) -- Police departments around the country are working to shield their radio communications from the public as cheap, user-friendly technology has made it easy for anyone to use handheld devices to keep tabs on officers responding to crimes.

The practice of encryption has grown more common from Florida to New York and west to California, with law enforcement officials saying they want to keep criminals from using officers' internal chatter to evade them. But journalists and neighborhood watchdogs say open communications ensure that the public receives information that can be vital to their safety as quickly as possible.

D.C. police moved to join the trend this fall after what Chief Cathy Lanier said were several incidents involving criminals and smartphones. Carjackers operating on Capitol Hill were believed to have been listening to emergency communications because they were only captured once police stopped broadcasting over the radio, she said. And drug dealers at a laundromat fled the building after a sergeant used open airwaves to direct other units there - suggesting, she said, that they too were listening in.

"Whereas listeners used to be tied to stationary scanners, new technology has allowed people - and especially criminals - to listen to police communications on a smartphone from anywhere," Lanier testified at a D.C. Council committee hearing this month. "When a potential criminal can evade capture and learn, `There's an app for that,' it's time to change our practices."

The transition has put police departments at odds with the news media, who say their newsgathering is impeded when they can't use scanners to monitor developing crimes and disasters. Journalists and scanner hobbyists argue that police departments already have the capability to communicate securely and should be able to adjust to the times without reverting to full encryption. And they say alert scanner listeners have even helped police solve crimes.

"If the police need to share sensitive information among themselves, they know how to do it," Phil Metlin, news director of WTTG-TV, in Washington, said at the council hearing. "Special encrypted channels have been around for a long time; so have cellphones."

It's impossible to quantify the scope of the problem or to determine if the threat from scanners is as legitimate as police maintain - or merely a speculative fear. It's certainly not a new concern - after all, hobbyists have for years used scanners to track the activities of their local police department from their kitchen table.

David Schoenberger, a stay-at-home dad from Fredericksburg, Va., and scanner hobbyist, said he understands Lanier's concerns - to a point.

"I think they do need to encrypt the sensitive talk groups, like the vice and narcotics, but I disagree strongly with encrypting the routine dispatch and patrol talk groups. I don't think that's right," he said. "I think the public has a right to monitor them and find out what's going on around them. They pay the salaries and everything."

There's no doubt that it's increasingly easy to listen in on police radios.

One iPhone app, Scanner 911, offers on its website the chance to "listen in while police, fire and EMS crews work day & night." Apple's iTunes' store advertises several similar apps. One promises to keep users abreast of crime in their communities.

Though iPhones don't directly pick up police signals, users can listen to nearly real-time audio from police dispatch channels through streaming services, said Matthew Blaze, director of the Distributed Systems Laboratory at the University of Pennsylvania and a researcher of security and privacy in computing and communications systems.

The shift to encryption has occurred as departments replace old-fashioned analog radios with digital equipment that sends the voice signal over the air as a stream of bits and then reconstructs it into high-quality audio. Encrypted communication is generally only heard by listeners with an encryption key. Others might hear silence or garbled talk, depending on the receiver's technology.

The cost of encryption varies.

The Nassau County, N.Y., police department is in the final stages of a roughly $50 million emergency communications upgrade that includes encryption and interoperability with other law enforcement agencies in the region, said Inspector Edmund Horace. Once the old system is taken down, Horace said, "You would not be able to discern what's being said on the air unless you had the proper equipment."

The Orange County, Fla., sheriff's office expects to be encrypted within months. Several police departments in the county are already encrypted, and more will follow suit to keep officers safe, said Bryan Rintoul, director of emergency communications for the sheriff's office.

In California, the Santa Monica police has been fully encrypted for the past two years and, before that, used a digital radio system that could be monitored with expensive equipment, said spokesman Sgt. Richard Lewis.

Still, full encryption is cumbersome, difficult to manage and relatively rare, especially among big-city police departments who'd naturally have a harder time keeping track of who has access to the encryption key, Blaze said.

The more individuals or neighboring police agencies with access, the greater the risk that the secrecy of the system could be compromised and the harder it becomes to ensure that everyone who needs access has it, Blaze said.

Relatively few local police departments are actually encrypted, Blaze said, though some cities have modern radio systems for dispatch that are difficult to monitor on inexpensive equipment. The systems can, however, be intercepted with higher-end scanners.

"I would not be surprised if a lot of departments that do it would switch back to non-encryption. The practical difficulties of trying to maintain an encrypted system at scale start to become apparent," he said.

Some departments have studied full encryption but decided against it, including police in Greenwich, Conn.

"Because we've always retained the ability to encrypt traffic on a case-by-case basis when we need to, in a community like Greenwich, I think the transparency we achieve by allowing people to listen to our radio communications certainly outweighs any security concern we have," said Capt. Mark Kordick.

And some departments have tried to compromise. The Jacksonville, Fla., sheriff's office leased radios to the media, allowing them to listen to encrypted patrol channels. That practice ended last summer out of concern about maintaining the confidentiality of radio transmissions, said spokeswoman Lauri-Ellen Smith.

In D.C., Lanier says the department is stepping up efforts to advise the public of developing crimes through Facebook, Twitter and an email alert system. Officers will use an unencrypted channel starting next month to alert the public to traffic delays, said spokeswoman Gwendolyn Crump. But the chief has refused to give radios to media organizations, which continue to assail the encryption.

"What about the truly terrifying crimes?" Metlin, the news director, asked at the hearing. "What if, God forbid, there is another act of terrorism here? It is our jobs to inform the public in times of emergency."

Rick Hansen says he's been listening to police communications since he was an adolescent and says efforts to shut them make government less transparent. The Silver Spring, Md., man says sensitive information could be kept off the airwaves on a selective basis.

"Yes, it's a concern - and it's something that can be addressed through proper procedures and processes as opposed to turning out the lights on everybody," he said.

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