Have you tried a pair of noise-cancelling headphones?
When turned on, noise-cancelling headphones automatically play the opposite sound frequency to noise around you. It dispels any noises physically but the sound it tells you so that you can hear clear sounds.
However, conventional noise-cancelling headphones cannot distinguish important alerts from noises. Thus, you can miss the siren whistled by a car approaching you fast.
Then, it is desirable that noise cancelling is turned off in a risky situation. Amazon is developing a solution to this issue, according to the media.
International Business Times: Amazon is working on noise-cancelling headphones which could save your life
Amazon’s new product can recognize some special noises, such as someone’s voice to call you, emergency alert, and so forth. Even when you concentrate on your work, you will never miss the key-phrases because the headphones recognize them.
Amazon seems not to let this product on sale. There are many usages of suspended noise-cancelling system. Workers in a factory, or even in an airplane, can wear noise-cancelling headphones to reduce their stress.
On the other hand, I do not think suspended noise-cancelling will be necessary for daily use. Current headphones cannot eliminate noises completely. I can hear the message in a station when wearing headphones.
But, in the near future, people will enjoy virtual reality systems frequently. In this situation, perceiving external situation when danger is approaching is crucial. Suspended noise cancelling should be mandated to be attached with such systems.