The 2017+ CX-5 and the 2018+ CX-9 have a different TPMS system. Previous models have an indirect system that uses the ABS wheel speed sensors to measure if the wheel is spinning faster due to the tire losing diameter (from low tire pressure). This system uses the reset button.
The newer models use a direct system that has the pressure sensors mounted with the valve stem, inside the wheel. When tire pressure reaches a minimum value set by the manufacturer, the sensor triggers a TPMS warning light.
https://www.tiresplus.com/tires/tire-buying-guide/tpms/
Both systems have their pros and cons. I like the direct system because it tells me that I might have low tire pressure before I even put the car into gear. I also never had to do a TPMS reset procedure when I swapped my winter wheels for my summer wheels. After swapping the wheels, the TPMS light never came on. As easy as it gets. I mean, it's more expensive overall, but it's also much safer and much easier to use. Could still be improved by having individual pressures shown somewhere in the infotainment, but that's a fault on Mazda for not implementing the feature, not the TPMS system.
As a sidenote, the OEM sensor for the 2018+ CX-9 is P/N BBM2-37-140
B. I found a used set of sensors on eBay with P/N BBM2-37-140
A. A Mazda service rep confirmed that the used set is a Mazda OEM part that simply comes from a different supplier. I paid $60 USD for 4 "A" sensors, and they work perfectly in my set of summer wheels. I believe these P/Ns also work for the CX-5 and probably the Mazda6 as well.
