| 摘要 |
<p>PROBLEM TO BE SOLVED: To prevent malfunctions by animals or the like, to make destruction difficult and to lower a cost. SOLUTION: When a door 14 and a window 12 are closed and a fan 6 is operated, since air inside a building 4 is discharged to the outside of the building by the fan 6, an air pressure inside the building 4 lowers. Thus, a difference is generated between the air pressures inside and outside of the building detected through tubes 18 and 20 by a differential manometer 8 and the differential manometer 8 outputs electric signals corresponding to an air pressure difference. In the case that the door 14 and the window 12 are kept closed, the air pressure inside the building 4 is almost fixed and the size of the electric signal outputted by the differential manometer 8 is almost fixed as well. When the door 14 and the window 12 are opened in the state, a space inside the building 4 are communicated with the outside through them, the air pressure difference between the inside and outside of the building is reduced and the electric signal outputted by the differential manometer 8 changes. An alarm generation means 10 detects the opening/closing of the door 14 and the window 12 on the basis of the change pattern of the electric signal and generates an alarm.</p> |
