That is not the brake pad "sensor" , wear indicator is a more proper term and they are attached to the brake pad itself , what your pointing at is the ss guide (or pad seat) your pads move on , perhaps your pads are stuck in these guides and are wearing them out , it is a common problem in rust prone areas , rust builds up under the guides and pinches the pads and then they can't release , and also makes your caliper sieze because that doesn't move when pads are pinched either .
Its imperative every season tire change out the caliper holder is removed and ss guides removed and rust removed from underneath them , I also put a light coating of syn brake lube on the surface before reinstalling the ss guides, this prevents rust,
Ask me how I know , got lazy one year after putting new Toyota pads on the front and rear and didn't take everything apart for my regular ritual just slapped the pads in and ran , smelled brakes one day ripped everything apart to see what was going on and had to pound rear pads out of holders with a hammer the rear pads were 80% gone and fronts had 20% gone this was only after about 30K KM