I put an airtag on my bike. I put it in my tool bag. I used to leave the tool bag on the bike thinking it wouldn't be a big deal if someone stole it. I disguised it as unattractive by putting it in a grocery bag and putting the grocery bag in the basket which is on the rear rack. That worked OK until I needed to visit my mother in law in the emergency late at night. I ended up staying at the hospital overnight, and I found my toolbag stolen. I'll never leave it out again, because it turns out that replacing everything in it cost over $100. Lesson learned. I watched where the airtag was for a while. It ended up in a housing project on the Lower East Side of Manhattan. Then nothing. Either someone removed the battery or assigned it to someone/something else. I'm not sure if that's possible. I decided not to wander throughout the project of apartment buildings to see if I could run into someone with my toolbag.

Attaching an airtag to a bike seems like a challenge. You want it to be hidden, and you also don't want to shield the electromagnetic energy with metal. I've seen gadgets you can use between the bottle cage mount and the bottle, and maybe it's mildly inconspicuous. I'm not sure.