It won't disable the alert on the thief's phone (if they use an iPhone or an Android with the tracker app), however it doesn't really need to as the alert could actually be beneficial in convincing the thief to simply abandon the bike then take time to find & disable the tracker all while they are being tracked and the owner (or ideally the police - though in practice they are useless) can show up at any moment. Even better if they get the alert once they've already brought it home as they're definitely better off moving the bike away from there rather than having the trail stop at their place.