mschwett 

unlike other trackers, an airtag will work if it's near just about any apple device that has a connection at all. if there's literally no cell service, no internet + wifi, no nothing, then it won't work. but if, let's say, you rode past a parked car and someone sitting in it DID have cell service, the location should update. similarly, if you go into a store which has wifi, and someone in there has an iPhone. or other apple device, or a cafe with wifi and wired internet (again, even without cell service.)

if the ride locations do not have some frequency of buildings with internet, cell service, public wifi, etc, then the airtag won't work and nothing except a satellite communicator will. something like a garmin inreach/inreach mini/acr bivy would work in theory. seems like overkill, depending on the level of concern.