What is a telephone ring down you may ask! They have been used for years as dedicated commu- nications paths between two standard telephone sets. Over a single pair, with a phone at either end, merely going off hook with one phone, im- mediately rings the other phone. When picked up, you have a complete intercom path to talk. No dialing necessary! What are they used for? Well, on the intercom or communications side they are commonly used for elevator phones, guard post hotlines, door entry phones in homes and office, and on commercial job sites for rugged intercoms. But it just starts there! Can be used to test ringing, answering, and signal path conditions of devices, two wire off premise extensions, PABX to Key System tie lines, and more. Measures 5/8 x 4¼ x 2½ inches and is totally encapsulated in UL 94V-0 flame-resistant epoxy resin for long reliable operation. Ringing pattern is selectable to continuous ring; 1on 1off; 2on 1off; 2on 4off.