They are fine. The only thing that triggers the sensors is when the brake pads get low enough to expose the sensor contacts to the rotors...the metal rotors complete the circuit to the sensor wiring and cause the brake pad indicator on the dash to light up...that's it.

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2009 ML350 (106K) - Family vehicle
2001 CLK430 Cabriolet (80K) - Wife's car
2005 BMW 645CI (138K) - My daily driver
2016 Mustang (32K) - Daughter's car