The part I like the most about the Airtags is that they tell on you if you try to use them for nefarious purposes. Granted it only works if the person has an Apple phone but it's still neat.
AirTag is designed to discourage unwanted tracking. If someone else’s AirTag finds its way into your stuff, your iPhone will notice it’s traveling with you and send you an alert. After a while, if you still haven’t found it, the AirTag will start playing a sound to let you know it’s there.
Of course, if you happen to be with a friend who has an AirTag, or on a train with a whole bunch of people with AirTag, don’t worry. These alerts are triggered only when an AirTag is separated from its owner.