Lost my main keyring last year, for the first time EVER. A diligent retracing of my steps enabled me to find it, but since it had been dropped along the edge of a cornfield, I think it was pure luck that I spotted it.
So— I went out and bought a set of Key Ringer key finder devices (available at fine stores and Amazon everywhere). They're fob-sized, come in a set of two, and me and my wife each carry one. They will not communicate with your phone or a network or anything like that, they can only call each other, but when the button is pressed, the other one rings LOUDLY, manufacturer claims 300 feet, which I wouldn't bet on with my ears. So far, although we tested them after purchase, we haven't had a real incident.
Way cheaper and less hassle than replacing keys.
NB: It's easy to say "don't lose your car keys." That works until it happens. Human beings make mistakes, the only thing we can do is make whatever happens manageable, and I think the best advice in this thread is to always have a spare key— never go with just one.