An on-hook EOH indicating telephone includes a parallel set detector, an EOH signal detector, and an indication module to activate a configurable audible and/or visual alert indicating that another telephone is off-hook and should be hung up. The audible alert may be a unique ringing of the otherwise...http://www.google.de/patents/US6603855?utm_source=gb-gplus-sharePatent US6603855 - Cordless phone notification of extended off-hook using parallel set detection
