thank you for your help, but i am new to this so i dont exactly know how to connect a relay in a circuit and which pins to connect and can you also suggest which relay to use, and the other thing is that i tried bunch of simple circuits like the one you gave me, and they work fine, but the problem is once the laser light touches the photocell the alarm stops it doesnt continue sounding...
is there any way that i can use the buzzer on the last schematics, i am by changing the value of the capacitor or something...
and i didnt get the circuit from colin55