You can set a silent alarm for the Philips health band via  the app. When the alarm goes off, the health band will vibrate and show the alarm icon. Stop the alarm by tapping on the display twice. If you want to snooze, wait until the alarm passes. After 9 minutes the alarm will go off again.

Note: When you set an alarm in the app, make sure you sync with the health band. After syncing, the health band will show an alarm icon on the display. The silent alarm is now set.