Abstract: An improved infrared detector system includes a pair of thin film thermopile sensing elements that receives reflected energy from aspheric reflectors that are designed to provide optimum energy resolution. An absorbing coating can be placed above the sensors and extending beyond the periphery to improve the signal to noise ratio. A high gain low noise D.C. amplifier is coupled to the output of the infrared sensing elements while a high pass amplifier and low pass amplifier are designed to pass an amplified signal in the frequency range from approximately 0.2 Hz to 15 Hz. Finally, a combined peak detector and time dependent integrator summing amplifier circuit provides an enabling predetermined threshhold detection gate that requires either a predetermined large signal level or a multiple of small electrical signals within a preselected interval to produce an alarm enabling signal.