PURPOSE: To monitor burglars at a window and a door with one crime prevention set switch by receiving the set output of a crime prevention set circuit and starting measurement of the time required for normal entrance and exit at the time of opening the door and operating a sound emitting device after the elapse of this time.

CONSTITUTION: When a crime prevention set switch 11 is made, the set output is outputted to a crime prevention set circuit 1, and a window open detecting circuit 2 and a door open detecting circuit 3 get ready to receive the detection output of a window sensor 21 and that of a door sensor 31 respectively. A timer 32 starts measurement of the time required for normal entrance and exit at the time of opening the door in this state; and when the door is immediately closed, the timer 32 is reset and a sound emitting device 5 is not operated. If the door is kept open by an unlawful trespasser, the timer 32 expires and the sound emitting device 5 is operated. If the window is opened by the trespasser, at the same time the sound emitting device 5 is operated. Thus, burglars are monitored in two positions, namely, at the window and the door by one crime prevention set switch 11.