Apple products communicate with each other even if they don't know each other, so an airtag will utilize the cellular of a nearby iphone in order to get information to apple's servers. I think google has a tracker that does something similar.
Its easy to imagine that previous generation tracking devices that sends its information across a broader range than an airtag will need to be larger battery thus being larger.
Its easy to imagine that previous generation tracking devices that sends its information across a broader range than an airtag will need to be larger battery thus being larger.