Today the ACLU, the ACLU of Connecticut and the Electronic Frontier Foundation once again took a stand against warrantless cell phone tracking, in a friend-of-the-court brief submitted to a federal judge in Connecticut. Cell phones are not just communications devices, they're tracking devices. Your cell phone provider can generate a continuous stream of location information, and many providers store this information for months or even longer.

This data is law enforcement's best friend. It's also a highly sensitive portrait of a cell phone user's life, tracing their movements wherever they go for an indefinite period of time. The proper way to reconcile these two interests is to require the government to get a warrant and show probable cause before tracking.

That is what we argued in our brief today. We hope the judge gives serious weight to the privacy interests at stake and rule that a warrant is required.

There is an especially interesting wrinkle in this case. The government got tracking information, not just for the criminal defendant, but for 179 other people. Although the details are still unclear, because the government's surveillance application is apparently under seal, it appears that to figure out who was involved in the crime, the government took the dragnet approach of getting location information for this vast number of people. We've heard rumors of this approach before — when law enforcement tracks everyone in what it calls a "community of interest" — but this is a rare public confirmation that it takes place. This sort of mass, generalized surveillance is worrying because it raises the prospect that many, many innocent people are tracked.

This needle-in-a-haystack approach to government scrutiny of our private lives cannot be what the framers of our Constitution envisioned. Courts and Congress should put a stop to this. Congress is currently considering reforming the electronic surveillance laws , and this "community of interest" approach should be at the top of its list of practices to be ended.