Ringdown (Telephone) : An Automatic ringdown circuit consists of two phones at different locations. When either phone goes off-hook, the one at the other end instantly rings
Wikipedia, The Free Encyclopedia, Glossary of firefighting terms, Wikimedia Foundation, CA, USA 2012. http://en.wikipedia.org/wiki/Glossary_of_firefight ing_terms, (Fr Srvc - Amer) {510}