Traditionally, mid infrared detection has been performed using black body sources and filters. With the availability of infrared LEDs, which emit between the 2 - 5 micrometers wavelength, solid state gas cells can be designed which eliminate the broad spectrum problem of black body source and allow ac signal detection without mechanical chopper wheels. Dedicated microprocessors also allow other advantages, including over-sampling and, in certain applications, emitter low power mode to reduce power consumption. Results are shown for gas cells to detect carbon dioxide and hydrocarbons. LED optical gas cells are applicable to systems that require low power drain, small size, log-term stability and/or fast warm up time. Laser Monitoring Systems Ltd has developed a family of infrared LEDs with narrower optical bandwidth that can be optically modulated by electrical pulses. These infrared LEDs can thus replace the thermal source, bandpass filters and chopper wheel of the conventional monitor, giving a solid state, lower powered, fast response and contact instrument.