Finger Ring, "Social Polling"

Finger Ring is a system in which a cell phone decides whether to ring by accepting votes from the others in a conversation with the called party. When a call comes in, your phone first determines who you're discussing with by using a decentralized network of autonomous body-worn sensor nodes. It then vibrates all participants' wireless finger rings. Although the alerted people do not know if it is their own phones that are about to interrupt, each of them has the possibility to veto the call anonymously by touching his/her finger ring. If no one vetoes, your phone rings.

This system of "social polling" shifts the burden of deciding whether to interrupt away from the phone and towards the humans who are actually involved in a conversation.

A work by Stefan Marti, who also developed the amusing Cellular Squirrel (via).