Why does my iphone 4 keep randomly vibrating?

I turned off the notifications for all apps but it still vibrates.

Might be your email. It's gives a short little vibrate when you get new mail without anything popping up on the screen

Set destruct security sequence activated. Tou have 72 hours from the moment of activation to cancel or your battery will overheat and melt tour mobile device. Just text your gamma six security password to your local police station to cancel. Otherwise, be sure to remove the device from your pocket and keep it away from flammable or explosive materials.