The headline for this link is incorrect: the Court did NOT rule that a warrant is necessary for police tracking.
So what was the government trying to do? They really wanted the Supreme Court to rule that installing this GPS receiver was not even a SEARCH within the meaning of the 4th Amendment. The Court said no, this is a search. In the future, they will subject similar GPS installations to 4th Amendment scrutiny.
But on the warrant issue, Scalia explicitly wrote the Court will not answer the question of whether the government needed a warrant on page 12 of the opinion. Why? "The Government did not raise [this argument] below, and the D. C. Circuit therefore did not address it... We consider the argument forfeited."
So what was the government trying to do? They really wanted the Supreme Court to rule that installing this GPS receiver was not even a SEARCH within the meaning of the 4th Amendment. The Court said no, this is a search. In the future, they will subject similar GPS installations to 4th Amendment scrutiny.
But on the warrant issue, Scalia explicitly wrote the Court will not answer the question of whether the government needed a warrant on page 12 of the opinion. Why? "The Government did not raise [this argument] below, and the D. C. Circuit therefore did not address it... We consider the argument forfeited."