We expect our cell phones to do a lot these days: make calls, check e-mail, take photographs, play music, surf Web sites, let the government track your every move. But civil liberties groups have a few questions about that last feature, and have filed a lawsuit seeking to force the Department of Justice to respond to a Freedom of Information Act Request submitted late last year, seeking documents about the practice of using mobile phones as homing beacons.

The complaint brought by the American Civil Liberties Union and Electronic Frontier Foundation seeks to compel the release of "all records pertaining to [the government's] policies, procedures and practices followed to obtain mobile phone location information for law enforcement purposes," especially when that information is sought without a warrant. The original request for expedited release of the records was made last November, to no avail, in the wake of press reports that federal law enforcement officials were routinely requesting location information for investigative purposes. Cell providers are required to be able to pinpoint a phone's location under "Enhanced 911" rules originally intended to aid police and paramedics when a mobile user called 911.

Most judges who have considered such requests have insisted that federal agents obtain a probable cause warrant to track suspects, as they would be required to do if they wished to wiretap the suspect's conversation. But in 2005, a federal judge in New York ruled that cells could be tracked under a far looser evidentiary standard.

Traditionally, courts have drawn a sharp distinction between the content of a telephone call and information about a call. Records of the numbers that have called or been called by a particular phone can be obtained relatively easily, via a trap-and-trace or pen register order. The call itself, however, requires a traditional Fourth Amendment warrant supported by probable cause. Justice Department guidelines suggest that investigators hew to the stricter standard when seeking to pinpoint a suspect, but the government has also argued that the laxer standard—requiring only that the request be supported by "specific and articulable facts"—may be appropriate when less precise geographical information is sought.

The ACLU and EFF are hoping that the release of internal memoranda and policies will shed some light on the prevalence of such requests, and the level of judicial scrutiny to which they are subject. Thus far, they have been ignored or rebuffed by the offices to which they have sent requests.