Anyone who watches TV crime dramas knows that law enforcement agencies track people through their cellphones.

But what the American Civil Liberties Union found out about how widespread such surveillance is by local police and sheriff's departments is still eye-opening.

Even more alarming, only a few agencies nationwide reported that they bother obtaining warrants based on probable cause before tracking someone's cellphone. The ACLU's position is clear: "That is what is necessary to protect Americans' privacy, and it is also what is required under the Constitution."

Based on its findings, it's difficult to argue that point. It should be plain, but apparently needs to be stated: Not every person is a potential suspect and authorities shouldn't be able to determine by themselves, without any oversight, that cellphone tracing is justified or necessary.

To pierce the secrecy shrouding the practice, 35 ACLU affiliates across the country filed more than 380 Freedom of Information Act requests last August with local law enforcement agencies, including more than 50 in California.

The ACLU of Northern California asked 20 agencies – including the Davis and Sacramento police departments and the Sacramento County Sheriff's Department – for their policies, procedures and other information.

To its credit, the Sacramento Police Department was the most transparent.

It said it almost always seeks court orders or search warrants for tracking cellphones. According to figures it released, tracking was used 177 times between 2005 and 2010 – rising from 14 in 2005 to 51 in 2010.

To their discredit, Davis police and the Sacramento sheriff were far less forthcoming. Davis police insisted it did not have much of the information requested, while the Sheriff's Department repeatedly denied the requested information, citing public safety exemptions to the public records law.

Nationwide, while about 200 agencies responded to the ACLU, nearly half the agencies rebuffed the information requests. That's a shame. At the very least, police and sheriff's departments should be willing and able to tell the public the general parameters of what they do, without jeopardizing their investigative techniques.

Somehow, law enforcement officials are much more willing to talk about how cellphone tracing is a powerful tool to locate fugitives, as well as in child abductions, drug investigations and other cases.

In January, the U.S. Supreme Court unanimously ruled that police violated constitutional protections against unreasonable search and seizure by planting a Global Positioning System device on a suspect's vehicle for an extensive period without a warrant. But by a 5-4 split, the high court declined to go further, for instance, by placing any limits on GPS tracking of cellphones.

Lawmakers in Sacramento and Washington, D.C., don't have to wait for justices to act.

The ACLU and Electronic Frontier Foundation are co-sponsoring a measure to require that California law agencies obtain a probable-cause warrant before they can get location information from cellphones and other devices. Sen. Mark Leno, a San Francisco Democrat, will carry Senate Bill 1434.

Bills with similar goals are pending in both the U.S. House (H.R. 2168 introduced by Rep. Jason Chaffetz, a Utah Republican) and Senate (S. 1212 by Sen. Ron Wyden, an Oregon Democrat). Those bills have languished since being introduced last June.

If you value your privacy, let the Legislature and Congress know you want action.

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