Optimum sensitivity detects leaks of 0.03 to 0.06 oz/year. Automatically self-calibrates to neutralize background contamination. Sensor life up to 200 hours or more. Sensitive to both R-12 and R-134a refrigerants. Certified to meet SAE J1627. High/low switch for accurate diagnosis of both large and small leaks Features high-performance heated-diode sensor technology! Detects leaks as small as 0.4 oz/year. Automatically self-calibrates to neutralize background contamination. Sensitive to both R-12 and R-134a refrigerants. Certified to meet SAE J1627High/low switch for accurate diagnosis of both large and small leaks. Variable-intensity audible alarm plus flashing LED help pinpoint leaks fast. Flexible metal probe holds its position in tight quarters. Easily replaceable foam filter protects sensor and pump. Includes replacement filters, (2) D cell batteries and rugged storage case. Self-calibrating - hassle free. Detects small leaks 0.4oz/yr - accurate. Good for R-12/R-134a - easy access. High/low sensitivity switch - superior engineering. Low battery indicator - reliable.