The PIR sensor used in the circuit will detect human IR radiations, when the sensor detects the human radiations its output goes high and activates the UM3561 IC. The UM3561 is a four siren sound generator IC and in this circuit we are only using one of its siren. At the output of the UM3561 IC a BD140 transistor is used to amplify the output siren sound of the IC. The operating voltage of the circuit is 5V to 12V DC.
There are many techniques to make a security alarm for example it can be made by using laser systems, infrared systems, touch sensors, vibration sensors etc. But in this circuit we have used a PIR sensor module to detect the entry of a person in the restricted area. The circuit is very easy to build and using
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