| 摘要 |
A portable security system is based on maintaining wireless communication between two or more plastic cards within a defined range. In the simplest form, a first card intermittently transmits an identification code to a second card. The second card compares that code with a code in an internal register, and on matching those codes, transmits a return code to the first card. The first card compares the return code with a code in an internal register, and on matching those codes, resets a timer. If the timer is not reset during a defined number of transmissions by the first card, an alarm circuit is activated. One card is attached to a valuable object such as a wallet on the person, and the other card is placed elsewhere on the person; theft of the object from the person results in activation of the alarm circuit. In an advanced form, a master card communicates with a series of slave cards; each of the slave cards is attached to a different valuable object on the person.
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