| 摘要 |
<p>The burglar alarm has a series of switches located close to each other which are responsive to the application of a magnetic field. One of the switches terminates current flow to a sentinel current device while the others initiate current flow. The sentinel current device operates to supply voltage for an alarm circuit when it conducts only. Thus, in order to render the device ineffective, one must know how to apply a magnetic field to the terminating switch only without activating any of the switches that initiate current flow. The switches are all located close together so that special knowledge is required to cut off supply voltage to the alarm circuit.</p> |
