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US9969404(TOYOTA ENG & MFG NORTH AMERICA [US])
Additional ones of sensors 28 may detect the presence or absence of a driver's hands on the vehicle steering wheel, the presence or absence of a vehicle occupant in a particular seat (for example, occupant detection sensors 28 a ), and the presence or absence of the driver's feet on one or more of the accelerator, brake and clutch pedals.

US9690963(COVIDIEN LP [US])
[0003] This disclosure generally relates to the detection of the presence or absence of objects tagged with transponders, which may, for example, allow the detection of retained medical supplies during medical procedures.