alt Hacker NewsI remember having to take my car in to adjust the aiming of the headlights after it didn't pass inspection. So we used to take things like this seriously. I just had my car inspected last month, I don't even remember them hitting the horn. I'm guessing they pretty much just shove a sensor up the exhaust pipe and call it a day while accepting your payment.
No shoving sensors required, the data is all in the ECU accessible over OBDII interface. The car knows if it’s compliant in real time using the sensors it already has.