From what I have read, The Fieldpiece SLR2 has a heated diode as well as infra red but is more expensive than the SLR8. The diode is buried inside the main body and cannot be replaced by the owner (Or maybe if you are a electronics guy) The life expectancy is around 10 years or less depending upon usage. The SLR8, which I have, and not yet tested,(Just got it) has a replaceable diode at a cost of around $50 or a little more. It seems to me that the SLR8 is more economical without having to add dye to a system to check for leaks, which some say can degrade HVAC components. However, having said that, after 10 years with an SLR2, who's to say that their might be an I-Phone app for leak detection. I'm just sayin'