Hearing damage occurs as a result of both the level of noise exposure and the duration of noise exposure. The louder the sound the less time that is required to cause hearing damage. For example at 85 decibels it would take two hours exposure in a day to cause any hearing damage, however at 95 decibels it would take around 10 minutes.
The Apple watch will monitor noise exposure and can send alerts when certain exposure limits are reached.
The noise monitor will be a feature available in the forthcoming WatchOS 6 software which will be launched in autumn.