From the Ubicomp 2005 demos, there is this extremely cool feature:
GETA SANDALS: KNOWING WHERE YOU WALK TO by Shun-yuan Yeh, Keng-hao Chang, Chon-in Wu, Okuda Kenji, Hao-hua Chu (National Taiwan University)The GETA sandals are Japanese wooden sandals embedded with location tracking devices. By wearing them, the GETA sandals can track anywhere a user walks to. The GETA sandals work both in the indoor and outdoor environments. The motivation for the GETA sandals is to create a location system that needs minimum infrastructural setup and support in the environment, making it easy for deployment in everyday environments. In our system, a user simply has to wear the GETA sandals to enable his/her location tracking. This is in contrast to most of the current indoor location systems based on WiFi or ultrasound, which need to setup access points, fixed transmitters and receivers in the environment. The GETA sandals track a user’s location using a footprint-based method. The footprint-based method uses location sensors installed underneath the GETA sandals to continuously measure the displacement vectors formed between the left and right sandals along a trail of advancing footprints. By progressively adding up these displacement vectors, the GETA sandals can calculate the user's current location anytime anywhere. Although the footprint-based method has the advantage of being a mobile and wearable location tracker, it has a drawback of accumulative error over distance traveled. To address this problem, the footprint based method is combined with a light RFID infrastructure to correct its positioning error over some fixed distance.
There is just this picture which is not quite informative:
