Abstract: There is disclosed herein an improved card reader for a security system utilizing a central controller and a plurality of card readers for controlling traffic through critical doors in a facility. During normal operation, the card readers read card data and send it to the central controller. The central controller makes the decision whether to grant or deny access based upon a comparison of the card data and data kept in memory regarding persons who are authorized access to certain areas. The central controller then sends a "Go" or "No Go" message, i.e., whether or not to grant access, to the reader after the access decision is made. The improved reader includes means for storing the authorized identification code data for persons who will be allowed access during times when communications between the card reader and the central controller are not working.

Abstract: A line monitoring system is disclosed which provides particular advantages to security systems having remote terminals. This system provides both a reduction in the required power for the line monitoring task and also increases the level of line security by generating a calculated response at the remote terminal, which calculated response could not be accidentally produced by a faulty remote unit. Futhermore, the calculated response at the remote unit greatly reduces the likelihood of clandestine entry at the remote site.