http://www.kk.org/quantifiedself/2010/05/eric-boyd-and-his-haptic-compa.php

'Here is Eric Boyd's talk about the device he built called North Paw - a haptic compass anklet that continuously vibrates in the direction of North. It's a project of Sensebridge, a group of hackers that are trying to "make the invisible visible".'

The technology itself is pretty interesting; see also http://www.wired.com/wired/archive/15.04/esp.html