I'd assume that the device will be obvious once the wrapper is open. Such a tracker requires batteries with enough power to driver a transmitter, and a reasona

I'd assume that the device will be obvious once the wrapper is open. Such a tracker requires batteries with enough power to driver a transmitter, and a reasonably efficient antenna. That means it has to be a significant physical size. If fact, it wouldn't surprise me if the only thing in the wrapper is a golden coloured tracker emblazoned with the word's "you won!", and the winners task is to wait for Nestle to come to him and deliver the 10000 pounds and missing chocolate bar (tough luck if you had the munchies). If fact, it would be quite fun evading the "Nestle police" for as long as possible, leading them on a merry chase across the UK.