We have to make a miniproject as part of my engineering course. I chose the above burglar alarm. I thought that there were some mistakes and I have made some changes (therefore some things are written in black). I did be grateful if you guys could confirm whether the circuit will work theoretically and practically. Let me know if I have made some mistakes. Here IC2 uA 741 is wired as a sensitive comparator ,whose set point is set by R6 & R7.The voltage divide by LDR and R9 is given at non inverting pin of IC2.At standby mode these two voltages are set equal by adjusting R9.Now the out put (pin6) of comparator will be low.Transistor Q1 will be off.The voltage at trigger pin of IC1 will be positive and there will be no alarm.When there is an intruder near the LDR the shadow causes its resistance to increase.Now the voltages at the inputs of comparator will be different and the out put of IC2 will be high.This makes Q1 on.This makes a negative going pulse to trigger the IC1 which is wired as a monostable multivibrator.The out put of IC1 will be amplified by Q2 (SL 100) to produce alarm.