The CIA and NSA have been developing a system of a brain implanted "chip" which would monitor the activity of criminals.
Joseph A. Meyer of the National Security Agency (NSA), ... suggested the use of electronic implants in almost all Americans who have been arrested...for any crime. ...They would be monitored continually ...
The devices would be similar to those advocated for use in dogs, for the purpose of identifying lost dogs.http://www.petfinder.com/dogs/lost-and-found-dogs/how-pet-microchips-work/http://www.amazon.com/Pet-Tracking-Microchip-Implant-Administration-Veterinarian/dp/B0002YFROI/
They could allow tracking of pedophiles (or anybody else).
Another reference for this is The Mind Manipulators
, by Alan W. Scheflin and Edward M. Opton, Jr.
The Mind Manipulators_ by Alan W. Scheflin and Edward M. Opton, Jr., published in 1978, is a fascinating account of the technologies of mind manipulation that are being used to subvert man's freedom and reduce him to a slave of his manipulators. Although somewhat dated, this book nevertheless remains very important for those who wish to understand the technological advances which have made possible mind manipulation and mind control on a massive scale.
* note: Puffferfish doesn't think this is a good idea, he's just reporting on what's going on these days.