We're using linear resonant actuators, rather than the ERMs normally found in wearable devices and personal electronics, because they allow us to have precise control over the intensity of the vibration we're creating. We take advantage of this and the psychological phenomenon of tactile illusions in order to create the sensation of vibrations that actually move from one place to another on the surface of your skin--allowing us to convey an upcoming turn or the passage of time just through your sense of touch.