To make initial registration of a suitable magnetic force level according to a combination of a magnetic sensing element and a magnet in actual use, and to set window opening/closing determination thresholds.

A window opening/closing monitoring device determines opening or closing of a window by comparing the magnetic force level detected by a window opening/closing detecting Hall sensor 46, with the determination threshold and carries out radio transmission. A locking monitoring device 78 determines opening or closing of a lock by the comparison between the magnetic force level detected by a locking detecting Hall sensor 48 and the determination threshold and carries out radio transmission. A rank table 88 stores the relationship between rank information set according to the output characteristics of the Hall sensor and amplification gains. A gain control section 76 changes the gains of an amplifying circuit to obtain gains acquired from the rank table 88 based on the rank information of the Hall sensor when started.

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