Activation of any indicator (LED/alarm) using voice signal is an innovative application of sound detection technique. During the testing and circuitry we experienced that there is a difference between expected efficiency and actual performance. The HPF output is not ideally noise free. The amplification should be 100 times. The reference voltage must be 0.45 volt. The absence of peak detector circuit not hampers the working of the system. 100 ohm resistor is necessary for LED protection.