| 摘要 |
PROBLEM TO BE SOLVED: To detect manipulations made on a switch by providing two lead switches in parallel closing a contact, when the first lead switch goes into the magnetic field of a magnet portion, opening a contact when the second lead switch goes into the magnetic field of the magnet portion, and placing the magnet portion so that it is installed in proximity to only the first lead switch when a window and a door are closed. SOLUTION: When this magnet switch is manipulated during a guard, a window and a door are closed, and contacts of both first and second lead switches 1a, 1b are closed during the defense. When a malicious third party bring in a magnet 6 by himself close to a lead switch portion 1, the second lead switch 1b goes into a magnetic field of the magnet 6 to open the contact, so that an alarm-sending apparatus 4 detects that no current is flowing in a loop of a lead wire 2 and issues an alarm to a remote guard center. This magnet switch can detect manipulation made on this sensor.
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