I think—and I'm speaking not so much from experience but based upon my intuition as an engineer—if you have a system like a GPS system, which can actually log the individual's position on a minute-by-minute basis, that represents a fairly large data file of information that needs to be transmitted and sorted and digested by some individual who assesses the response, whereas one of the RF systems or biometric systems tends to work based upon a single sample of information that's sent to a monitoring centre. So the amount of data that goes to the monitoring centre is far less, and obviously far less effort is required to understand what it means. It tells you where you are now and that's it, not where you've been, etc.
On February 14th, 2012. See this statement in context.