Many years ago, on this very forum, somebody suggested a good DIY project was to knock up a device which exploded when 3 or 4 of it's kind were gathered within a few yards, and fitting them to "Hobby" type touring caravans (if you know what they look like, you'll know why ...).
Rather than piss around with "is it/isn't it" worry over tracking, surely the easiest thing to do is to drive the vehicle into a Faraday cage and thence into a Faraday barn ?