activate the alarm on the required level of darkness. An LDR is used as a dark sensor. Output of the IC is connected to an 8 ohms speaker through a 4.7uF electrolytic capacitor that is working as a filter. The audio / alarm tone can be changed by changing the value of the 0.05uF capacitor. The circuit can be operated from 9V to 12V DC, you can use any type of battery or power supply.  For best results fit the circuit is a suitable enclosure. Make sure to make a hole in the casing for the LDR to sense light and dark.

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This is a project of a dark activated alarm circuit using a 555 timer IC. It will produce an audible alarm when there is not light on the surface of the LDR. The circuit is wired around a famous 555 timer IC. The IC is used in an astable multivibrator here.  The 10K variable resistor is used to adjust the circuit to
Dark Activated Alarm Using 555 Timer IC