Use a Mute Ringtone to Mute IPhone Alarms
Regardless of whether your iPhone is turned off, if you have an alarm set, it will beep. How-To Geek points out that a silent ringtone can solve this potential problem, so you will still receive vibration without ringing.
The process here basically requires you to use a ringtone without real sound. How-To Geeks published their own to simplify the process. Once this ringtone is on your iPhone, just set it as your alarm sound and you’re good to go. This can be useful if you need an alarm to go off during a meeting, in a restaurant, or anywhere else where you don’t want nasty bells ringing just to remind you to do something. Personally, I have it set for my timer, which I usually only use to remind myself when the parking meter expires. Go to How-To Geek for a complete guide.
How to Set an iOS Alarm to Vibrate but Not Beep | How-To Geek