Review on LotFancy Freon Leak Detector: Ultimate HVAC Refrigerant Gas Leakage Tester for Home & Professional Use - CFCs, HCFCs, HFCs, R134a R1234yf R410a R22 R11 Compatible, High Accuracy & Indicator Light by Charles Alfian

I bought these for my husband a few days ago and they arrived today. Super fast shipping and the best price I could find anywhere! I saw some reviews saying this sniffer doesn't work. It almost didn't work for us until my husband figured out a few things. 1) It takes 4 (four) batteries, not 2. When you open it it only seems to hold 2, but you have to pull it out and put 2 more batteries on the back of the holder. 2) Make sure you insert the batteries correctly. My husband uses Kirkland batteries which look like they have 2 positive ends. He found that one of the batteries was upside down and now the thing works like magic! He said it was amazing how sensitive he was! That's a great buy guys!