| 摘要 |
The device has a permanent magnet (A) that is mounted near an interior face of an opening frame (O). A magnetic field detector is mounted on the opening frame, where the detector is formed by two knife switches that are positioned on the opening frame, and the switches face away from each other. The detector is provided in rectangular in shape. An alarm and/or indication unit is activated depending on a state of the detector, which indicates if a window is opened or closed. |
