.....an ultrasonic leak detector?

Wooo not so simple for me.. maybe I can ask my friends..I'm not so able with electronic parts 

I built a very effective leak detector. (Don't laugh it works well)
Take one of the cardboard center rolls your cloth or plastic came on.The 2 inch stuff will do.
Cut one piece 15 inches long another 5 inches.
Now cut a 45 angle on one end of each piece.
Join them together with duct tape.
Hold the small end up to your ear and go around the bag looking for leaks.
It took me like 5 minutes to make while my bag was leaking so I made it in a hurry.
You will be amazed how loud the leak sounds with this detector.
I also have a doctors stethoscope which does not work as good as the card board detector!
Patent Pending
Fred