The pressure in a given pneumatic device is usually sensed by a pneumatic switch. This uses a spring device that is constricted as the pressure increases. The more the spring is pushed back, the more it turns the outside dial that shows the precise pressure within the tank. Sometimes the pounds per square inch (psi) of tanks is measured digitally for greater accuracy and effective transportation, while with other systems air is being gathered and compressed continually, and an analog dial may be a more effective and durable option.

Uses of pneumatic pressure switches include:
Switching off an electrically driven gas compressor when a set pressure is achieved in the reservoir
Switching off a gas compressor, whenever there is no feed in the suction stage.
in-cell charge control in a battery
Switching on/off an alarm light in the cockpit of an aircraft if cabin pressure (based on altitude) is critically low.
A pressure switch is a form of switch that closes an electrical contact when a certain set pressure has been reached on its input. This is used to provide on/off switching from a pneumatic or hydraulic source. The switch may be designed to make contact either on pressure rise or on pressure fall

PNEAUMATIC switch is called pressure switch

Uses air to open or close the gate. normal electrical switch uses contacts (NO and NC) for connecting or disconnecting electrical circuit. however, in mechanics, where we have to operate some valves or cylinders using air, we have to use pneumatic switch which is controlled by an electronic circuit. when one needs to open or close the gate, we have to apply or remove the air so that the valve gets opened or closed.
even hydraulic switches are used in mechanical switching applications which work on oil and not on air. principle of operation is same.

Electrical contact is made through the application 0f pneumatic (Air) pressure medium.