Two Port Modular Exclusion-Privacy Device. Viking's Teleguard privacy devices prevent your phone calls or fax and modem transmission from being interrupted if someone accidentally picks up another extension. Teleguard devices can also secure against internal eavesdropping by any other extension equipped with a Teleguard device. Viking's Teleguard products protect the device that accesses the telephone line first by denying other Teleguard equipped devices access to the line until the call in progress has been terminated. Incoming calls will ring all devices simultaneously, but the device that answers first denies any other Teleguard equipped device access. Applications Prevent interruptions and replace dedicated phone lines for: Point-of-sale terminals Modems Fax Machines Home and business telephones Credit card machines Replacement for Proctor Model #41412, 41403 and 41404 Features Line powered Modular or punch-down installable One and two line devices Compatible with analog lines with 12V DC or higher talk battery Transparent operation One year warranty Made in the USA.