Choose an Earplug of Slightly Bigger Size to Avoid Whistler. 1 x Pair of Hearing Aids. With bluetooth function, you can listen to songs and make calls. If You Hear a Howling, Check the Ear (Silica Gel) Is Appropriate and Whether the Size of Plug Is Tight, the Appropriate Choice of Earplugs and Plugged, Make Sure No Air Leakage.