The byron smartwares b323 portable wireless plug through door chime kit has a 50 metre operating distance it has a choice of two melodies and offers volume control it features self learning codes that will keep the code even when the batteries run out and are replaced its plug through feature means that there is no loss of socket another mains powered object can to be powered by plugging into the chimes socket it also contains a battery powered portable chime that can be taken with you anywhere