In response to the growing privacy concerns, local law enforcement agencies in Maine are now required to have a warrant to track cell phone activity.  Passed on Tuesday, LD415 reads: "a government entity may not obtain location information without a valid warrant issued by a duly authorized judge or justice."

It defines government entity as "a state or local agency," clarifying that federal agencies are not bound by the warantless cellphone tracking state laws.

The law goes on to mandate that in the event that law enforcement agencies do obtain a search warrant, that they notify the user within three days of tracking "unless they can prove that secrecy is necessary in order to delay the notification for an unspecified period."

Unlike many laws attempting to protect the privacy of cell-phone users, Maine's new warrantless cellphone tracking law extends the requirement for a warrant to the history of location information, meaning that law enforcement agencies cannot snoop into a users phone records for past locations or check-in information.

This is a clear departure from the Department of Justice's interpretation of the Fourth Amendment as made clear in a brief filed on the applications of the United States of America for historical cell-site data. In the brief, the DOJ specifically argues that "customers have no protected privacy interest in historical cell-site records," citing United States v. Miller (1976).

Their reasoning lies in the fact that historical cell-phone records are stored by cell phone companies, or third-parties, and “the Fourth Amendment does not prohibit the obtaining of information revealed to a third party and conveyed by him to Government authorities" (United States v. Miller).

There is only one state ahead of Maine in the fight against warrantless cellphone tracking: Montana. Historically becoming the first in the nation to pass such legislation in late June, Montana's law also requires law enforcement to obtain a probable cause warrant before tracking a person "based on his or her cell phone location information, social networking check-ins, or via a GPS tracking device in a criminal investigation," the ACLU reports.

On the privacy front, other states making history include Texas, which just became the first state to enact legislation requiring law enforcement to obtain a warrant in order to sift through people's personal emails.

With states taking the lead with privacy protection laws, it's only a matter of time before Congress responds.