Simple Advance Burglar alarm from dual-op amp Circuit . Device such as burglar alarms and sirens, whose basic purpose is to monitor certain conditions, make enjoyable projects because of the verity of sounds they can generate. Figure 1 shows a simple siren/alarm circuit using a dual-amp MC1458, audio amplifier LM380, and a 1-W speaker. The dual op-amp is used as a signal generator that produces square, pulse and triangular or sawtooth wave froms. The operation of the circuit is as follows. The A1 and A2 op-amps make up a waveform generator in which the output of A1 is a square wave or pulse waveform and that of A2 is either a triangular or sawtooth waveform. The potentiometer R2 controls the frequency as well as the type of output waveform of op-amps A1 and A2. The switch SW1 connect the output of A1 or A2 to the audio power amplifier LM380, this in turn drives the speaker. Although not used in the circuit of figure 1, a potentiometer may be connected between (+) and (-) inputs o...