The consensus here seems to be that the FBI crossed the line from passive to active tracking, and should have needed a warrant, when they entered his property t

The consensus here seems to be that the FBI crossed the line from passive to active tracking, and should have needed a warrant, when they entered his property to place the GPS device into his vehicle. Tracking you by something like GPS on your cell phone doesn't require physical interaction with your property. The effect is similar, though. What's the difference?