Approximately 91% of Americans use cell phones these days. While they're convenient and it's even hard to imagine life without them anymore, they're also voluntary tracking devices. And U.S. law enforcement agencies are increasingly obtaining that data that tracks you.Earlier this week, Congressman Ed Markey revealed that, in 2011, nine major mobile phone companies - including the Big Four: Verizon, AT&T, Sprint, and T-Mobile - responded to a staggering 1.3 million law enforcement requests for subscriber information, including calling records, text messages, and location data.Sometimes the companies hand over users' data when law enforcement agencies have a warrant or issue a subpoena. Other times, they do so when there is an "exigent request", which is a sworn declaration from an officer that there’s an emergency. And other times they do so in the form of a "tower dump", which tells police ALL of the mobile phones that pinged a tower in a given time period.This is news that ought to concern everyone. Pundits like Wired's David Kravets immediately called forand new requirements for companies to have tohow many times a year they get such requests for users' data, and how they respond to them.That's all well and good, but the issue is so complex that it's going to require a lot more to protect users' privacy in a meaningful way than just requiring public reporting.For starters, the Supreme Court has already ruled that the government cannot use GPS tracking devices without a warrant . In fact, the issue here is not government-tracking at all; it's the fact that individuals are voluntarily carrying around tracking devices with them everywhere they go, willfully agreeing to allow their mobile carriers to track all their activity. So that information is already collected and we have all repeatedly given our consent to it. Legally, the government can't directly track us without a warrant, but private companies can (with our consent).So the real question is: Once we've agreed to allow ourselves to be tracked by private companies, to what extent can (or should) government agencies be granted access to that information that's already been collected?What's needed is for Congress to not only require more transparency, but to also strengthen individual privacy laws by clarifying exactly under what circumstances warrants or subpoenas are needed, and exactly under what circumstances they aren't.Politically, it seems as though there ought to be room for bipartisanship here. Small-government conservatives and libertarians can view this issue as a potential intrusion on individual liberty. Meanwhile, liberals and progressives can frame it in terms of strengthening consumer protection laws.It's been clear for quite a while that the law needs to catch up with technology. Here's an opening.