Satellite tracking is a search
In Grady v. North Carolina, the US Supreme Court on March 30, 2015, held that the satellite monitoring of a person, at least when it is accomplished in part by affixing a tracking device to the person's body, amounts to a search under the 4th Amendment to the U.S. Constitution. Grady grew out of an earlier decision, US v. Jones, 565 US ____ (2012) which held that police engaged in a "search" when they placed a GPS tracking device on a suspect's car.
In the Grady case, Grady challenged the requirement under North Carolina law that, as a repeat sex-offender, he be required to wear a tracking device and be subject to continuous satellite monitoring for the rest of his life as an "unreasonable" search that violated the 4th Amendment's ban on unreasonable searches and seizures.
The North Carolina courts had rejected his claim simply upon the ground that the monitoring requirement was part of a civil, not criminal, enforcement action and therefore the 4th Amendment did not apply. The Supreme Court disagreed, reaffirming the 4th Amendment's application to all government action be it civil or criminal in nature.
Interestingly, what was not before the Court was any argument that imposing a continuous satellite monitoring requirement is in fact reasonable under the 4th Amendment. While this case continues the current trend of extending the protection of the 4th Amendment to new technology it does so on the very limited grounds of: A) Some physical trespass upon the body or property has occurred, and B) leaving open the question of whether the application of such monitoring to recidivist sexual offenders is reasonable.
Most interesting for future litigation will be the application of this case, and others preceding it, to the technology based monitoring of citizens that does not require a physical intrusion upon that person's body or property. For example, if continuous satellite monitoring of a person were capable based on facial recognition it is not entirely clear that such monitoring would be found to constitute a search for 4th Amendment purposes.