A system for monitoring dialled numbers is disclosed which provides a subscriber with a record of numbers dialled over his telephone line or lines. The system provides a monitoring unit inductively coupled to each line which tapes the dial pulses as they are dialled. Aslo included is a control processing...http://www.google.com.tw/patents/US4013839?utm_source=gb-gplus-share專利 US4013839 - System for monitoring dialled telephone numbers
