Hi Michael,
I was curious about the Airtag and looked it up. I found this in a PCMag review:
"A prime concern about AirTags and other tiny tracking devices is that they will be used to track people, not devices... To address this, the Find My app will alert you on your Apple device if it detects a AirTag not attached to your Apple ID—and separated from its owner—traveling with you. You're then given the option to disable that AirTag, or to play a sound so you can locate it. "
Sounds like a thief with an iPhone would be able to find/disable the Airtag if they were aware of the possibility there might be one in the car.
Meyer