Abstract: A security system for cordless telephones prevents unauthorized telephone lls over telephone lines. The system includes a base unit and a cordless handset unit which must share common information for proper operation. To prevent an unauthorized user in possession of a handset unit from easily matching a security code stored in the base unit and thereby obtain dial tone therefrom, the security code in the base unit is transferred to the handset unit while the handset unit is in a mating cradle in the base unit. Transfer circuits in the base unit and the handset unit respectively transmit and receive the security code and also an operating frequency channel over a direct-current charging path provided for charging of a battery in the handset unit whenever the handset unit is returned to the cradle.

Abstract: The disclosed PBX integrity arrangement utilizes a specialized processing operation to provide an integrity check for communication devices and trunk facilities connected to a PBX. The integrity check determines (1) whether a user of a device or a trunk facility is permitted access to one or more PBX operations or (2) whether the PBX operation meets expected conventional PBX call establishment conditions. If access is prohibited or an atypical condition is present, this access or condition may indicate permission tampering, device or trunk facility misuse, malfunction or unauthorized PBX user activity. The occurrence of any one of the above conditions produces an immediate response which either remedies the occurrence or provides notification of the occurrence of the condition to a PBX administrator.

Abstract: A circuit (16) is designed to prevent unauthorized access to a remote device such as a computer (10) over a communications system such as a telephone network (12). A remote computer terminal (13) is connected to the telephone network (12) through a conventional modem (14). At the remote location of computer (10), circuit (16) is connected between computer (10) and another modem (15). Circuit (16) is also connected to the telephone network (12) to receive a signal therefrom which connects modem (15) through circuit (16) to computer (10) to temporarily access the same. The connection, however, is disconnected after a predetermined time period unless circuit (16) receives a second signal from the telephone network (12) before the expiration of that predetermined time period.

Abstract: A system provides for the validation of users of a trunked radio system. The system includes a controller and at least one microcomputer-controlled repeater module for user identification and validation. Each repeater module includes a tracking filter for removing unwanted noise from the two-tone signal sequentially transmitted by the user's radio as well as a digital signal processor utilizing a novel filter algorithm to quickly and reliably identify and validate user group tones. If identified as a valid user, the repeater module allows the call to pass. If the identity and validity, i.e., a paying customer, of the user are not validated by the repeater module, the repeater is shut down and the user is unable to communicate, and only hears alert tones from his speaker.