... over at The Liberty Papers
. Do the police need a warrant to attach a GPS tracking device to your car in order to follow you?
Normally, I'd say yes. If you are going to follow someone everywhere they go in public, I'd say you should need a warrant. Doubly so if you are actually attaching something to them or their property in order to do so. I doubt the law actually agrees with me on this point, though, as it considers movements in public to have no "expectation of privacy"...
I do think that there's an additional threat raised by cheap surveillance devices such as were used here, and as cell phones have now become. It's expensive to hire enough police officers to do a full-time stakeout on a suspect, so there are pressures to avoid spending time and effort on that unless it's very likely to be productive. But if you can do it easily and cheaply with technology, we have to fall back on legal protections to prevent a true surveilance society.
There are some other issues at play in the specific case being described in the article, though. The person being followed was a registered sex offender, targetted for the operation due to being on the sex offender registry and living near the scene of repeated sexual assaults, and appears to be guilty (he was arrested allegedly committing another attack and there were not any further attacks after his arrest). Seems to be they would have trouble getting a warrant on those facts if they had tried, but even so got the right person.
One of the relevant Supreme Court cases includes the following quote:
A person traveling in an automobile on public thoroughfares has no reasonable expectation of privacy in his movements.
It's easy to agree with this principle when you would need to hire three people full-time to follow your target everywhere they went in order to make use of the lack of privacy. But in a modern surveillance state where toll roads use individually-identifiable RFID tags to record (and charge tolls on) individuals based on where they drive their car, the barrier to complete surveillance is a lot lower.