The testo 316-3 is our best refrigerant leak detector yet, and delivers dependable, rugged performance at a great value. The heated diode sensor provides sensitivity down to 0.15 ounces/year including the new refrigerant blends like R-410A, R-407C, and R134-a, allowing you to quickly locate refrigerant leaks. Just turn it on and start getting readings immediately. Thanks to automatic zeroing, the testo 316-3 is extremely fast, and can be used even in previously contaminated areas. The 316-3 has an LED indicator, automatic zeroing, and an audible alarm, all in a rugged housing.