Aloha cosmic,
I use one to find hard to locate air leaks on truck air brake systems mostly in the cab area. I know that it has to be in an enclosed area so that you won't pickup ambient or surrounding noises. But it still not 100% in finding an air leak, I still use a soapy pray solution or leak detector spray when I can't hear or pinpoint where the leak is coming from. For me if I had the chance again about purchasing my unltrasonic leak detector I probably would spend my money elsewhere. BTW I have the AccuTrak VPE ultrasonic leak detector kit w/ contact probe at the time of purchase I believe it was around $450
Aloha,
Keone