A search for neutrons from deuterium “cold fusion” systems (both electrochemical and high-pressure gas cells) was conducted in an underground laboratory using three highly sensitive neutron detectors composed of 3He gas proportional counter tubes embedded in polyethylene moderators. Any neutron emission from a test cell would be simultaneously observed in all three detectors in a known proportion. The counting system can detect random, continuous emission at a rate of <100 n/h, and short bursts of as few as 35 neutrons. None of the cold fusion systems tested emitted neutrons at these levels. Occasional anomalous groups of counts were observed in individual detectors that closely mimicked both continuous and burst emission. These anomalies were identified as spurious detector artifacts rather than true detection, because counts were not observed in the appropriate proportion in all three detectors. The use of multiple detectors simultaneously observing the test system in a very low background environment can effectively identify spurious artifacts that might otherwise be interpreted as evidence of neutron emission and may be essential to the demonstration of low-level neutron production from cold fusion systems.