Airtags use a CR2032 lithium battery: https://support.apple.com/en-us/HT211670
The FAA specifies both lithium ion and lithium metal batteries need to be in carry-on bags only, not checked: https://www.faa.gov/hazmat/packsafe/more_info/?hazmat=7
The FAA specifies both lithium ion and lithium metal batteries need to be in carry-on bags only, not checked: https://www.faa.gov/hazmat/packsafe/more_info/?hazmat=7