We have an AirTag in our dog's collar which is registered to my wife's AppleID¹ The first walk I took with the dog after she put it on the dog, I got a notification about an unidentified AirTag (which included her email address and I think phone number) following me.

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1. My single big complaint about AirTags is that they can't be shared between Apple IDs. Presumably that will be changed in a future software upgrade. Right now, only my devices can be used to find my things and her devices her things even though we can use Find My to find each others devices.