| 摘要 |
A property external security device having at least one light barrier is characterised by the cable-less laying of light barrier transmitters and receivers. The transmitters and receivers are equipped with their own energy supply, e.g. by means of batteries or, preferably, by means of solar generators. A central station which serves to sound the alarm is connected to the light barrier receivers in a wireless fashion, preferably by radio. In order to save operating energy, the optical transmitters and the radio transmitters are operated in a pulsed fashion.
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