Abstract: A detection circuitry designed to sense a composite signal of the type such as composite frequency shift keying (FSK) 50% amplitude modulated (AM) signal or pulse code modulated return to zero FSK type signal. The circuitry includes means for separating the composite signal into its constituent components and means for converting the separated signals into an amplitude envelope signal and a differentiated DC component. The circuitry includes a trigger circuitry for providing an output signal when the input thereof is of a predetermined polarity and amplitude and means including peak detection circuitry for applying the amplitude envelope and DC component so that the polarity of the differentiated DC component is applied to the trigger circuitry in the predetermined polarity so that the DC component is additive to the amplitude envelope, whereby the speed with which the trigger responds to the start and the end of the incoming composite signal is fast.