Design of FootIO is based on Rober's frame work of haptic instant message. By rolling the rod of the device forth and back users create a serious signals to ask the remote device to vibrate. This is like to create and express some emotional clue - hapticons (haptic emoticons) to the remote communication partner.
Reference: Riki Kawakami (2008) Instant Messaging and Haptic Presence. http://www.sis.uta.fi/~hui/mobile/papers/Kawakami-paper.pdf