The circuit uses a photoresistor to monitor the opening of the refrigerator door (the refrigerator's own lighting), and if it detects that the door has been left open for too long, it draws attention to this with an audible signal. The sound signal only sounds with a delay after the light is detected.
The buzzer turns on with ~1 minute delay.
Power supply: 9V DC
Quiescent current consumption: <1mA
Active current consumption: 15mA (when light is active)
Maximum current consumption: 41mA (when beeping)
The set contains parts to be soldered!

Assembly instructions: Assembly instructions