A pressure switch is a device that detects changes in pressure within a system and activates or deactivates electrical circuits based on those changes. It is commonly used in various applications, such as in HVAC systems, water pumps, and industrial machinery, to ensure safe and efficient operation. When the pressure reaches a predetermined level, the pressure switch will either close or open a set of contacts. This action can trigger alarms, start or stop equipment, or control other devices, helping to maintain optimal pressure levels and prevent potential damage to the system.