>>With the GPS you don't have to follow the person around though.

>To me that isn't anything more than a semantic difference. In one case it's electronic, in another it's in person. The end result is the same in that a record is kept of your whereabouts.

The same semantic difference exists between keeping an eavesdropper's ear to the door and bugging the room - and there's still a warrant required for the latter.

The substantial difference is that electronic devices leave a firm record, whereas the physical observer needs to type a report - and can be trusted or not. The electronic record is less suspect.