So wouldn't the thieves with iPhones also eventually just get a notification that they are being tracked and then know to search the bike for an air tag? If the thieves are doing this for the money, then they'd simply make sure not to take the bikes to a endpoint where they can be tracked too until after they have determined if it has such a tag.

Additionally, it just seems like all they'd really need to find out if it has an airTag is an RF detector of some sort. Which can be very inexpensive.