Note: This is a DIY kit, you need to assemble it, easy to install, not supply instructions.
When no light hits the photosensitive resistor, the transistor turns on and the buzzer gets the power to start tweeting. When there is light on the photosensitive resistor, the transistor is turned off, the buzzer is powered off, stop tweet. Transistor used here as an electronic switch.
Working voltage 3V
5 x DIY Infrared Laser Kit