Why does iPhone 5 vibrate Rondomly

[iMore Question]

Someone was calling me and it started to vibrate

 

[Just_Me_D]

Someone was calling me and it started to vibrate

If you have it set to both ring and vibrate then it'll vibrate when you receive a call.

 

[Sherry_B]

If someone calls you and the phone vibrates, that's not random. You have it set that way in the Notification settings.