PURPOSE: To aim at reduction in the number of parts through providing a single device with both a crime preventive function and a fire protective function by attaching a reed switch to a fixed substance, such as window frame and the like, and then attaching a magnet part and a heat-sensitive ferrite part to a movable substance, such as window and the like.

CONSTITUTION: A magnet 1 and a heat-sensitive ferrite 2, which are attached to a window 5, cause a magnetic flux in such a manner as the arrows so that the contact 3 of a reed switch 4 attached to a window frame 6 is closed. Subsequently, when the window 5 is opened, the magnetic flux of the magnet 1 stops passing through the switch 4, and the contact 3 changes to an opening state so that a detection can be made. While, in the case where the ambient temperature rises to more than the Curie point of the ferrite 2 with the window 5 closed, the ferrite 2 loses its magnetism so that the magnetic flux stops passing through the contact 3, and the contact 3 changes to an opening state so that an abnormality can be detected. Thereby, a crime preventive function and a fire protective function can be used jointly with each other, and the required number of parts can be reduced.