I. INTRODUCTION
Mobile devices, such as laptops, smart phones and PDAs, have become an essential part of our daily life. They are small and easy to carry but also powerful in computational and storage capabilities. Unfortunately, these merits also put them at risk. For example, because mobile devices are small, they usually are highly susceptible to theft, especially at public places like airport terminal, library and cafe. Recently, as mobile devices get slimmer and more powerful, the number of mobile device thefts surges. According to the FBI’s National Crime Information Center, the number of reported laptop thefts in 2008 rose with a 48 percent increase over the previous two years, from 73,700 to almost 109,000. On the other hand, keeping data secure in a mobile device is not just a daunting challenge, but a critical requirement. Unfortunately, a majority of the mobile device users do not take necessary actions to protect the data stored in their mobile devices. Therefore, the loss of a mobile device could mean the loss and exposure of sensitive information stored in the lost device, which may be much more valuable than the device itself. According to CNN, a laptop theft case in 2006 related to Veterans Affairs Department resulted in the exposure of millions of veterans’ personally identifiable information and costed the department 20 million dollars to settle the lawsuit against it. This demo implements a pervasive mobile device protection system with the help from sensing and wireless networking technologies. In the system, we deploy low-cost wireless devices at public places of our interest to form a wireless network infrastructure. Users and mobile devices carry special-purpose wireless sensing devices which work with the wireless network infrastructure to provide protection to the mobile device and the data stored in it. Specifically, the system has the following features: ² Context Awareness: sensors carried by users and mobile devices collect context information (e.g., proximity between users and mobile devices) and the system adapts its behavior properly and promptly to the context change. – Anti-theft Protection for Mobile Device: the system will alert the user (directly or multi-hop via the wireless network infrastructure) when it detects a potential theft (e.g., via proximity sensor and motion sensor). – Privacy Protection for User Data on Mobile Device: the system adapts the privacy protection level for user data on mobile device. For example, when a user is away from his/her mobile device, user data on mobile device shall be encrypted. ² Transparency: System adapts its behavior autonomously without requiring explicit user intervention or causing extra distractions to the user. II. SYSTEM OVERVIEW In our prototype (see Fig. 1), each laptop and each user carries a wireless sensor which runs on battery power supply. Each building such as library, shopping center, hospital, and airport has several infrastructure sensors installed at different spots to form an infrastructure sensor network. For each building, one separate infrastructure sensor network is formed and one central server is installed. Fig. 1. System Architecture Within an infrastructure sensor network, each laptop is monitored by its neighboring infrastructure sensors in the absence of its owner to detect suspicious activities. For example, suppose Alice enters a library. Alice’s sensor and laptop’s sensor join the infrastructure sensor network via an authenticated join message to neighboring infrastructure sensors. After joining the network, Alice’s and her laptop’s sensors periodically broadcast authenticated alive messages which can be heard by neighboring infrastructure sensors. Suppose Alice wants to leave her laptop in a reading room for a while to get some coffee in the cafe. Commanded by safety modes based on Alice’s proximity to her laptop, the laptop is locked automatically and sensitive information is protected by encryption. Further, the infrastructure sensors start to monitor her laptop. If moved by a thief, the laptop’s sensor can detect the motion and trigger an alarm with alert messages sent to Alice (directly or via infrastructure). If the thief destroys the sensor in the laptop, the infrastructure sensors will not receive authenticated alive messages from the laptop sensors, thus detect the abnormal phenomenon. They will report the problem to the central server, which in turn automatically sends an alert message to Alice and the security authorities.

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