| 摘要 |
A light-curtain alarm system is disclosed that provides to authorized persons uninhibited access to a protected item by automatically, temporarily deactivating the alarm whenever proximity of an authorized person is detected. Each authorized person carries a deactivating device that is detected at short range, preferably using radio waves or Bluetooth. Embodiments can track detection information, and/or distinguish between a plurality of deactivating devices, so as to track and/or control access to the protected item. The deactivating device can be included in an identification badge, and/or can be carried in a pocket or worn around a wrist or neck. The light-curtain can be generated using any combination of lasers and/or other light sources, light reflectors, and photo-detectors. In preferred embodiments, the alarm system can be configured to control access to a magnet of a magnetic resonance device, such as an MRI or NMR.
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