Nothing beats a visual inspection, whether it's to check for a sensor connection or brake wear.

That said, I wouldn't rely on parts sites to tell you what's on there. Many of them say my car has four, but they're only on the front. (The better sites suggest checking the car to be sure.) But they're cheap and easy to store, so no big deal.

I never understood the point of putting them on all four corners. Absent some kind of malfunction, the pads on the same axle will wear the same. (And a malfunction that would alter that likely would be noticed by the driver.)

That said, I really don't understand the point of putting only two sensors on the car, with both of them on the front. Maybe it's all the rage in Stuttgart?

Good luck with it.