If I get it right, then AirTags send a Bluetooth-signal to other iOS-devices within the reach of Bluetooth. The iOS-device then sends the received message to iCloud and iCloud then messages the owner.
Now, I ask myself: If I lose an item in an unpopulated area, like for example in a wood, would I benefit of having an AirTag attached to it? Even if it's very unlikely that someone with an iPhone passes by?
Yesterday I made an trial. I got the impression, that an iPhone memorizes the last location on which it had contact to a coupled AirTag. I'm I right there?
If that's the case then the AirTag would be still useful as marker, where I parked my car or where I lost my wallet.