A person-carried hydrogen sulfide instrument is adapted for use with a conventional SCADA system or other type of fault monitoring system normally intended for monitoring well-related conditions at a well site. In response to detecting an abnormally high concentration of hydrogen sulfide gas, the instrument triggers the fault monitoring system to record an H2S fault and convey that information to a remote computer. In some embodiments, the instrument includes a signal relay unit that listens to a conventional H2S monitor. The signal relay unit has a learning mode that teaches the unit to recognize an audible alarm from the H2S monitor. In response to bearing the H2S alarm, the signal relay unit emits a trigger signal to the fault monitoring system.