Such technology already exists in the form of a small transmitter that can easily be placed in a backpack or pocket. The batteries need to be changed periodically (I think it's weekly) and it also involves a subscription to a tracking service, much the same as GPS navigation services.
The problem is expense--the device itself is in the $100-200 range but the subscriptions are around $60/month.
Setting aside illegal violation of privacy...
Not so easy as you might think. It's difficult to put a GPS locator on a person because people change clothes. Also, the locators are relatively large, the size of maybe 3 fifty cent pieces glued together, so it's not like someone isn't going to notice something like that in their pocket or the hem of their coat.
What is more successful is putting a locator into a vehicle. The problem with that, of course, is that people don't always take the same vehicle all the time.
Tracking someone's movements via satellite photography can be done, so long as the person is outdoors (most people spend the majority of their lives indoors). The main problem with satellite photography is that there are not anywhere near enough photo-analysts to process the data they're getting right now. Computer recognition programs are rudimentary at best.
Big Brother isn't here quite yet but the day is within sight. It's time now to decide what the ethical limits of privacy are before that day arrives.
