The materials are simple: one battery case (mine is with a switch), 1 LED, 1 photoresistor
The LED is connected in series with the photoresistor (the longer the wire, the better will be, you will know why later). I connect them together for the convenience of demonstration.
Place it on the door with the battery case (PS: The photoresistor must be placed in a place where will be dark when the door is closed, be bright when the door is opened, otherwise it will have no effect)
I put it on the door like this for the convenient demonstration.
Close the door, no light, the LED is off
If there is light, the LED will be on
You can connect the light and battery case to your desk or bed.
It will be better to change the LED into a bell.
You will know if someone enters your room.
Source From:diy.elecfans
Translated By: Utsource
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