A leak detection system for a refrigerant circuit is provided. The refrigerant circuit is sealed and circulates a working fluid having a refrigerant (e.g., flammable refrigerant) and an oil. A reducing tag component is solubilized within the refrigerant. The leak detection system also includes a sensor for detecting the tag component if the refrigerant should leak from the refrigerant circuit. The sensor is highly sensitive to the tag component and thus enhanced detection is enabled. The tag component is stable in the working fluid and does not affect the flammability rating or performance of the refrigerant or oil. The tag component is present at a concentration of from about 50 ppm to about 35,000 ppm in the refrigerant. Methods of detecting leaks from refrigeration systems are also provided.