Ring Laser Gyroscope

The Ring Laser Gyroscope is a consumer device version of the Michelson-Gale-Pearson Experiment. The principle of operation of these devices is based on the Sagnac Effect, which was famed for showing that light changes velocity on a rotating platform. Like with the Michelson-Gale-Pearson Experiment, some have alleged that Ring Laser Gyroscopes have detected the rotation of the earth.

From a work titled The Sagnac and Michelson-Gale-Pearson Experiments (Archive) by Dr. Paulo N. Correa we read on p.5:

Essentially the tests saw wild results. There was almost no change to light's velocity in one test, and then a lot of change in another test. It is perplexing that the rotation of the earth would start and stop when tested at different times. Only through the statistics was it claimed that the experiment saw the rotation of the earth. The inconsistent results were ambiguous in nature and could offer no evidence of the shift in the phase of the light beams.

As stated above, the results of the Michelson-Gale-Pearson experiment were inconsistent and an algorithm was applied to get the desired result. If we are to say that the Ring Laser Gyroscope is the same device, then the same criticism would apply.

Cause of Noise
While inconsistent experiments are invalid as demonstration of any particular cause, one potential cause of the noise in these very sensitive devices is seismic disturbance. See: Ring Laser Gyroscope - Seismology

Further Reference

 * Ring Lasers - a brief history (Archive) - Describes that the Ring Laser Gyroscope is a Sagnac/MGP device.