Location tracking has far-reaching implications for the way we live, even if we don't think we've done anything wrong. Our recent report, " You Are Being Tracked ," shows that automatic license plate readers allow law enforcement to track every car on the road, not just those relevant to an investigation. This type of widespread tracking endangers our rights of protest and association and has the potential to reach deep into our lives and alter our daily decision making.

License plate readers are poised to become commonplace. As we note in our report:

...as license plate readers have proliferated, they no longer capture individuals' movements at only a few points. Increasingly, they are capturing drivers' locations outside church, the doctor's office, and school, giving law enforcement and private companies that run the largest databases the ability to build detailed pictures of our lives.

Knowing or suspecting that we're being watched can stop us from engaging in certain kinds of behavior, even when it's perfectly lawful. For example, it might affect our decision to go to a certain barber (what would my other barber say?), meet up with a friend (what would my mom say?), eat at a restaurant (what would my trainer say?), or take the scenic route (is it suspicious that I'm not using my normal route?). Surveillance changes the way we make daily decisions—the same way that a rapidly approaching police car in your rearview mirror may make you feel nervous even when you are driving completely lawfully.

And it doesn't necessarily matter that it's not your mom or your trainer behind the license plate reader pointed at your car. Once your location information is collected and stored by a third party, you have lost control over it, and there is no way to know whose hands it will end up in. We acknowledge this instinctively when we feel discomfort about being watched or followed by anyone, not just those who are most consequential in our lives. When people feel that their movements may be recorded, they feel less comfortable traveling freely and engaging in activities that might be controversial or stigmatizing, even when those activities are important or beneficial.

Even the police have acknowledged the chilling effects of surveillance. A 2011 report by the International Association of Chiefs of Police (IACP) noted that individuals may become "more cautious in the exercise of their protected rights of expression, protest, association, and political participation" due to license plate reader systems. The IACP report continues:

Recording driving habits could implicate First Amendment concerns. Specifically, LPR systems have the ability to record vehicles' attendance at locations or events that, although lawful and public, may be considered private. For example, mobile LPR units could read and collect the license plate numbers of vehicles parked at addiction counseling meetings, doctors' offices, health clinics, or even staging areas for political protests.

This chilling effect may be especially pronounced for license plate reader data collection, where information about where you travel can be used to infer information about who you are. In some cases, merely having your car parked in a certain area may be enough to gain law enforcement scrutiny. The IACP report remarks that it may be useful to know whether a car was parked near a domestic violence call or previous crime scene, whether or not the owner of that vehicle was involved.

Unfortunately, these examples are far from improbable. In New York City , police officers used unmarked vehicles with license plate readers to track congregants at local mosques. In Colorado, as one of our public records requests revealed (page 7933 of this document ), the Adams County Sheriff's Department demonstrated license plate reader technology by singling out music lovers for surveillance, sweeping a rave party and a concert at a country-western bar (first it's the line dancers, next they'll come for the swing dancers, and then the bedroom mirror dancers?).

In order to limit the chilling effects of this new technology, our report recommends a strict retention policy: