Using the Vibration API

Harness the device's vibration motor using the vibrate() method, accessible on the navigator object.

Simply pass in the number of milliseconds you want the vibration to last.

navigator.vibrate(1000);

You can also specify an array of values. Every other value will be interpreted as a pause.

navigator.vibrate([1000, 500, 1000]);

For this example the device would vibrate for one second (1000 milliseconds), pause for half a second, and then vibrate for one more second.

Firefox led the way with browser support for this one, but Chrome and Opera have joined the party too.

W3C Specification - Browser Support