Solid state relays (SSRs) are industrial-grade electrical components used to control older machinery with modern electric actuators. Unlike conventional electromechanical relays, SSRs are silent, require no moving parts, and require no external power source to function. SSRs detect electrical signals, then activate a solid state switching device, such as a field-effect transistor (FET), bistable flip-flop, or optically coupled switching mechanism, to switch current in the device. They are much more reliable than conventional relays, as they can endure considerably higher electrical loads with no power loss and longer life span under heavy usage. An industrial-grade SSR is designed for far harsher environmental conditions, typically employing a mounting system made of metal, such as stainless steel, to ensure durability in all conditions.