I use Airtags for this purpose with my car and my bicycle, but they're not designed for this purpose. You can pull the speaker coil out of them fairly easily, but they will still notify the thief that they're being tracked if they have an iPhone on them. Not ideal, but it beats having a huge epidemic of stalking.

They will also notify an Android phone if they have installed the app which Apple created for this purpose. I have to imagine thieves would know about this.

tssva

A thief can use the Apple provided app to discover if there is a tag, but I don't know that I would say it notifies them since unlike on an iPhone it would require the thief to actively open the app and perform a manual scan for the tag.

commoner

That's true for Apple's Tracker Detect app, but any thief or other user could simply use the free and open source AirGuard app on Android, which has more functionality than both Tracker Detect and the AirTag anti-tracking features built into iOS:

https://github.com/seemoo-lab/AirGuard

For example, AirGuard lets the user activate the alarm on any AirTag in range immediately without waiting any period of time. iOS and Tracker Detect only let the user do this if they determine that the AirTag is following the user, and Tracker Detect adds another 10 minute waiting period for no good reason.