Operators of gas detection systems used in safety-critical applications in the hydrocarbon processing, petrochemical and other industries are increasingly looking for rugged fixed, open path (line-of-site) gas detectors featuring high safety integrity with low levels of maintenance and total cost of ownership. Enhanced Laser Diode Spectroscopy™ (ELDS™) is a unique class of laser diode spectroscopy that includes techniques for increasing sensitivity and reliability for gas detection applications. The design of an open path gas detection (OPGD) system with ELDS can meet industry requirements for high safety integrity and low maintenance with two proprietary ELDS techniques: harmonic fingerprints and automatic functional testing of gas detectors. Harmonic Fingerprinting enables new levels of precision and reliability of target gas identification. Simulated gas detection enables simple, remote functional testing without the traditional requirement to apply a test gas to a detector in the field.