This is a video of Santa alarm. This video shows how to make a alarm when the refrigerator’s door is opened. The requirement to make this alarm is a 9V battery, the reed switch, magnet, wire and buzzer. This buzzer will buzz when the magnet is taken away from the  reed switch. Here is the tutorial video:

The red wire of the buzzer is connected to the red wire of the battery. The reed switch is connected to the black wire of the battery. The reed switch is normally open switch. Then attach the alarm to the refrigerator’s door. When the door open, the buzzer will beep.