In this paper we use the accelerometer of a smart phone to design and implement a fall monitor with GPS function for the user. We not only analyze the change of acceleration but also analyze the six typical actions of humans. These are going upstairs, going downstairs, standing up, sitting down, running and jumping. Then we compare the six actions with the characteristics of a fall. These are weightlessness, impact, immobility and overturning of the body. Our design is based on an open source system platform and the accelerometer in the smart phone. If there has been a fall motion our design provides the GPS functionality to obtain the location of the user and draws the help path on both the smart phones and the computers of his family, friends or help center immediately.