Mobile devices like laptops, iPhones and PDAs are highly susceptible to theft in public places like airport terminal, library and cafe. Moreover, the exposure of sensitive data stored in the mobile device could be more damaging than the loss of device itself. In this work, we propose and implement a mobile device protection system using sensors, based on sensing and wireless networking technologies. Comparing with existing solutions, it is unique in providing an integrated protection to both device and data. It is a context-aware system which adjusts the protection level to the mobile device dynamically according to the context information such as the user proximity to the mobile device, which is collected via the interactions between the sensors carried by the user, embedded with the mobile device and deployed in the surrounding environment.