This seems like a reasonable ruling.

Giving privacy-rights advocates and civil libertarians an important victory, a federal appeals court ruled that police conducted an illegal warrant-less search by planting a GPS device in a drug-case suspect’s car and tracking him for a month.

In ruling Friday that the police violated the suspect’s Fourth Amendment rights, the U.S. Court of Appeals for the D.C. Circuit said that by almost any measure, planting a GPS device, then following a person for several weeks conflicted with an individual’s reasonable expectations for privacy.

It will be interesting to see how the law develops for personal spying and private investigators.