The byron smartware b322 portable wireless plug in door chime kit has a 50 metre operating distance it features self learning codes and will keep the code even when the batteries run out and are replaced it comes with a portable chime that can be placed in a different room to the plug in chime it has a 80 85d b rating depending on the sound compatible with all byron db ranges the plug in chime is mains powered the push requires 1 x 23a battery included the portable chime requires 3 x aa batterie