Global Positioning Satellite (GPS) systems are by now a ubiquitous technology: we have them in most cell phones, we use them in our cars to get directions, and governments use them for a variety of purposes. One of those uses is to track people as they move about in their vehicles. DHS has authorized federal, state and local agencies to buy these technologies with their federal dollars. Take a look at the available products here.
While the ACLU of Massachusetts doesn't object to the use of GPS for legitimate law enforcement investigations --- when the police or FBI have obtained a warrant from a judge allowing them to track a suspect --- we have reasons to believe that law enforcement is increasingly using GPS tracking devices to follow people who are not suspected of having committed a crime.
That's what likely happened to Yasir Afifi, a 20-year-old American student from California. He discovered a tracking device on his car and posted pictures of it online. A little while later, FBI agents showed up at his door demanding their device. He has not been charged with any crime. But because the FBI's standards for domestic investigations have been steadily degraded over the years, the fact that he is not a criminal would not prevent the agency from investigating him.
The law around GPS tracking without warrants is confusing, with conflicting decisions coming down from various courts nationwide. The 9th Circuit Court of Appeals in California recently decided that law enforcement does not need a warrant in order to secretly place a GPS device on someone's car. But other courts have ruled differently, including the US Court of Appeals of the DC circuit. In that decision, Judge Douglas H. Ginsburg, writing for the majority, described why this kind of warrantless tracking is dangerous to our democracy:
A person who knows all of another's travels can deduce whether he is a weekly churchgoer, a heavy drinker, a regular at the gym, an unfaithful husband, an outpatient receiving medical treatment, an associate of particular individuals or political groups—and not just one such fact about a person, but all such facts.
The Obama administration has asked the US Supreme Court to address these conflicting decisions, arguing that the government needs to be able to surveil people in order to gain evidence against them, even when it has no proof of wrongdoing prior to the GPS surveillance. On June 27, 2011, the Supreme Court agreed to hear the case.
On January 23, 2012, the Supreme Court ruled that the government had violated the Constitution when they placed the GPS tracker on Mr. Jones' car without a warrant. Read more about this crucial decision here and here.