I am not sure what's with the tone of this comment, it seems a lot like a teacher who once told me I'd never be able to get a job if I put my feet on my desk, but, here I am.

(26) Baggage equipped with lithium battery(ies) must be carried as carry-on baggage unless the battery(ies) is removed from the baggage. Removed battery(ies) must be carried in accordance with the provision for spare batteries prescribed in paragraph (a)(18) of this section. The provisions of this paragraph do not apply to baggage equipped with lithium batteries not exceeding:

(i) For lithium metal batteries, a lithium content of 0.3 grams; or

(ii) For lithium ion batteries, a Watt-hour rating of 2.7 Wh.

https://www.ecfr.gov/current/title-49/subtitle-B/chapter-I/s...

For reference, a typical CR2032 has 0.1g lithium metal content and ~0.6Wh capacity.

https://data.energizer.com/pdfs/cr2032.pdf

1. you could always use the "oops, must have forgotten the airtag from my last trip :^)" excuse

2. The relevant authorities[1][2] seem to say that batteries in checked luggage is fine as long as it's in install equipment, so you're not violating any regulations that would get you reported.

[1] https://www.iata.org/contentassets/6fea26dd84d24b26a7a1fd578...

[2] https://www.faa.gov/newsroom/lithium-batteries-baggage

Do the AirTags have lithium ion cells?

I thought they have the no explosive cr2032 or thereabouts…

cr2032 are lithium, but not usually the same chemistry as rechargeable lithium ion. (side note, some cr2032 cells for use as battery backup for realtime clocks are actually rechargeable, which is pretty cool) However, as the sibling comment says, they are allowed because there is a threshold below which batteries are allowed.

a cr2032 is an example of a "lithium primary cell" meaning it's not rechargable, whereas "lithium ion" is rechargeable https://www.mpoweruk.com/lithiumP.htm