If someone's nicked your wallet, they'll take the money and maybe the cards then bin the wallet unless it's worth a lot in itself. Unless they're completely thick they will probably notice something conspicuous in it nearly 4mm thick with a 'Trackr' logo on it as being a tracking device or at least something that would be good to smash into pieces. More money down the drain.
If you're going out on the lash, use a money belt and only put in it what you actually need. Maybe one cashcard, your Oyster card, some notes and some change.