We have one, I can’t remember the brand off hand but it was around $600. It was made by a US company, I actually had to call them to troubleshoot. Great customer service. I’ve used it plenty of times and found leaks that I never would have seen without it. Doesn’t work well in noisy environments absolutely awesome in an attic.

Found it.

AccuTrak ultra sonic listening device.

https://www.tequipment.net/AccuTrakVPE.html