I like to put put my cell phone on vibrate mode and set the alarm for 5-10 minutes after I start masterbating and then lie on my stomach with the phone between my legs. I'll grind against my hand/phone until I get warmed up and wait for the vibrations. When they go off, it's usually a slight surprise and feels amazing. My phone vibrates in pulses for 1 minute before shutting off and sometimes I'll set the alarm several times, seeing how long I can hold off before orgamsing. It's fantastic.