I've just tried, it works: if the remote stays 4-5 meters away from the bike, the engine doesn't start.
But... if I go away 2-3 meters, a thief can jump on the bike, start the engine and go ! Then even if the bike is further than 5 meters, the engine wont stop ! ????
Sorry that doesn't work with the PCX.
Conclusion: the only 100% safe way to lock one PCX is to use the remote.