A method and apparatus for monitoring posture are disclosed. A first unit is attached to a first position on a user's body, and a second unit is attached to a second position on the user's body. A signal such as an ultrasonic signal is transmitted by the first unit to the second unit. In response, the...http://www.google.es/patents/US5469861?utm_source=gb-gplus-sharePatente US5469861 - Posture monitor
