Etymotic Research’s HD-15 High-Definition electronic earplugs is the ever-best gadget that can both protect your ears from loud noises and let people to hear when it isn’t noisy. Note that you can always have the earplugs in your ears, no needing to take them out or in from time to time.
The HD-15’s secret lies in the tiny microphones built inside, which instantaneously cause the plugs to block incoming sound waves if the noises are over a given threshold. But when the noise is ceased, the earplugs then let wearers to hear normally again. For people who have hearing problems, the earplugs may even amplify ambient sound by 15 decibels.