Electromechanical relays are devices that use an electromagnetic coil to open or close a set of contacts, allowing them to control a circuit. When an electric current flows through the coil, it generates a magnetic field that moves a lever or armature, which in turn either connects or disconnects the contacts. This action enables the relay to control larger currents or voltages with a smaller input signal. These relays are commonly used in various applications, including automotive systems, industrial machinery, and home appliances. They provide isolation between the control circuit and the load, enhancing safety and reliability in electrical systems.