| 摘要 |
Users of the system are each provided with an indicator module capable of presenting a display. An authorization module keeps track of which users are authorized to access a facility, such as a secured area or a parking facility. The authorization module sends messages, such as SMS messages, to the authorized indicator modules directing them to present a common valid display. The common valid display changes repeatedly over time, but, at any one time, the modules of authorized users all present the same display. A user may be granted or denied access based on whether the display on his module is the same as that of known authorized modules.
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