Pressure switches can sense pressure with the assistance of a variety of mechanisms, such as piezoresistive pressure sensors, elastomeric diaphragms, and pressure transducers. Piezoresistive pressure sensors are commonly employed by electric pressure switches; electric switches use them by converting the pressure level they sense into an electrical signal that can be read on a digital display.
When pressure reaches a predetermined level, whether it be rising or falling, on their input. Usually, the response garnered by a pressure switch is automatic.