A number of states already have laws preventing the police from prying on your phone’s location history without a warrant, but they just got another big boost from a court ruling.

Even if it is a vague information like the whereabouts of cell towers you’ve used, a California-based federal judge has determined that cops need those warrants, because you have a reasonable probability that your position data will remain private.

The judge says that cellphones can follow you anywhere, and transmit a lot of information. This location data may reveal much more about your life than you’d willingly share. This is accurate especially at home, and other private places where you have plenty of constitutional safeguards.

This isn’t the first ruling of the sort and is not legally binding. There’s no guarantee that officers across the US will ask nicely before trying to find out where you’ve been. However, it could have the police thinking twice about playing fast and loose with surveillance technology. They may not be so quick to track your phone, if they know that they risk losing their case.