> Note that the person who buys the 1-year devices every year pays 10x the "externality fees" as the person who buys the 10-year device. That may not be clear

> Note that the person who buys the 1-year devices every year pays 10x the "externality fees" as the person who buys the 10-year device. That may not be clear at time of purchase though. You could express this as an estimated rate per year, though. Both devices have a $50 externality fee. One has a 1 year warranty, 1 has a 10 year warranty, so the first has a $50/year externality and the second has a $5/year externality. Doing it by warranty period also helps prevent claiming a device should last much longer than it does.