| 摘要 |
<p>Telephone line access control (6) for preventing unauthorised outgoing calls on a telephone line (1). The control (6) includes means (10, 11) for monitoring dialling signals on the line, means (12) for encoding the monitored signals, means (14) for comparing the encoded signals with a memorized authorisation code, a bistable access mode control means (80) switchable between a first de-activated state permitting outgoing calls, and a second activated state preventing outgoing calls, and control circuitry (16) effective when the access control means is activated for temporarily interrupting the line connection when the encoded signals do not match the authorisation code, and for both temporarily interrupting the line connection and de-activating the access mode control means when the encoded signals match the authorisation code.</p> |
