Technological advances in signal processing and in circuits integration offer 
numerous perspectives in telemedicine and telemonitoring. Considering the 
increase of life expectancy, accurate and reliable assessement of modification 
and/or deterioration in the health status of a person is needed. One possible 
indicator is the "activity index" of a person. To compute such an index, 
previous studies have used accelerometers. Although these sensors are 
appropriate for the detection of postural transitions (e.g. Sit To Stand and 
Stand To Sit), they do not allow to detect changes of direction of a walking 
individual insofar as such activity occurs in a constant gravitation field. 
Within this context, the purpose of the present work is to investigate whether 
magnetometers can be used to monitor the changes of direction of a person.