Made by advance electron element. It can extend one exterior circuitry into four telephones to use (control by number of extension). And it can not increase the burden of circuitry of post office, each extension can listening and talking direatly.Between every extension, they always keep their work single, they don't break into the others, and keep secret while people talking. Nbsp; See more

Package Content : 1 x Telephone Extension Secrecy. Net Weight : 39g. "Overall Size : 8 x 5 x 1.7cm / 3.1" x 2" x 0.67" (LWT);Color : Off White". Connector Number : 4;Material : Plastic, Electronic Parts. Product Name : Telephone Extension Secrecy; Model : JL-184H.