What is NOT an effective way to detect the general area of a small leaks?

Electronic leak detector can detect the leak rates of about 0.5 oz per year. Ultra sound leak detector listens to the noise of gas leakage. Fluorescent leak detector detects the leak with the help of dyes. These dyes can cause strains on the equipment and foreign substances in dyes could invalidate the warranty. Also this method cannot be able to detect the immediate leak.