Solid state relay (SSR) is a non-contact switch composed of solid-state electronic components with high reliability, non-contact, no spark, long life, no noise, no electromagnetic interference, high switching speed. Electromechanical relays (EMR) is a kind of magnetic switch made up of multi-coils, movable elements, contact system etc. and it is easy to drive and widely used in all the areas. Then what are they differences? Which one is better?