System and method for determining the activity of a person lying down

A system for determining activity of a person lying down, comprising at least two processing pathways of signals at an output of at least one motion sensor substantially affixed to said person, wherein a first of said at least two processing pathways processes a first component comprising signals of low frequencies and a second processing pathway processes a second component of signals of high frequencies, said system further comprising:

• one or more processors;
• a first calculation module configured to calculate, using said one or more processors, a first variable representing a temporal variation of said first component, for at least an axis of said motion sensor;
• a second calculation module configured to calculate, using said one or more processors, a second variable comprising a Euclidean norm, along at least one measurement axis, of said second component;
• and
• an analysis module configured to determine, using said one or more processors, an activity of said person as a function of time using a hidden Markov model having N states corresponding to N activities respectively, said analysis module being configured for combining:
• conjoint probability density functions of said first and second variables, said probability density functions being defined for each state of the model;
• and
• probabilities of transitions between at least two successive states.