Air Tag Detection Range

The AirTag relies on Bluetooth and the Apple Find My Network to provide its location to the Find My app on your iPhone. The Find My Network literally consists of potentially millions of other iPhones.

Without trying to go into too many details, let's use your AirTag in Paris, with you & your iPhone in NYC. Let's say this AirTag is attached to piece of your luggage that was left behind.

• The AirTag's Bluetooth beacon transmits a signal approximately every 3-5 mins. It does so to conserve its battery life.
• If one or more iPhone(s), that is(are) participating in the Find My Network, gets within the tag's Bluetooth range (~30-40'), it will receive this signal, and then, relay its (the phone's location) anonymously to the Apple servers over the Internet. Obviously, that phone must have an active Internet connection either by a Wi-Fi or cellular connection.
• The Apple servers receive this location information, along with your tag's "ID", and forwards it to the Find My app on your iPhone.

So yes, in theory, the tag's range can be limited only by it being on Earth ... so Paris to NYC would be completely doable.

both are probable. The device itself has a limited range but any Apple device nearby can read/receive/share the location. So yes, a device left on a street in Paris, France can be seen in Paris, TX