Why doesn't the alarm sound when the timer's done?

We're working with Apple to fix cases where new customers ended up with a Notification Center setting for sound to 'off'.

Meanwhile, you can turn the sound off manually by going to 'Settings > Notification Center > OneHour' and turning the 'sound' setting to 'on'. This should be a one-time inconvenience that should be addressed once we find an exact cause, so take our apologies, and we'll keep you posted.