In this paper we present a context-sensitive security model for privacy protection on mobile phones. We describe the system TreasurePhone which implements this security model. The Privacy Protection is realized by spheres, which represent the user’s context specific need for privacy. That is, users can create any number of spheres and define which services and data are accessible in each sphere. TreasurePhone integrates context information for supporting authentication and activation of spheres by locations and actions. A basic hierarchy is used for determining which location should be activated based on the associated sensor value. Categories and Subject Descriptors H.4 [Information Systems Applications]: Miscellaneous General Terms Human Factors, Security, Management Keywords Privacy, Data Security, Mobile Phone