tracking settings such as timer setting for checking the device position through GPS and GSM cell. The timer properties include a date interval, the time of the day to start and stop tracking, the interval, in minutes, that the GPS and GSM cell store the current position. The administrator will be able to set an interest point as well as the boundary radius around it. The tracking tool must compare the received GPS coordinates with the security radius. If the device is detected out of the radius, a warning will be sent via SMS to a predefined emergency number with the date, time, current GSM cell and GPS coordinates. If the GPS receptor is unable to get the current position, the tracking tool will store the last known GPS coordinates and the actual GSM cell. The SIM card detection is a tool that allows only authorized SIM cards in the device. By enabling detection, the tracking tool can detect an unauthorized SIM card in the device and will be able to send a warning notification via SMS to a predefined emergency number with the current GSM cell and the present or latest GPS coordinates. Moreover, through the received SMS, the emergency number also receives the phone number of the unauthorized SIM card. For the user’s safety, the application will allow the sending of distress calls via SMS to a predefined emergency number. The mTracker features a contact editor, where the administrator can create, remove or edit a contact to be set as an emergency contact that shall receive the alerts. The application interacts with the contacts through Microsoft Pocket Outlook to stay stored in the PDA memory and not in the SIM card memory. We have also developed the mTrackerMap, a PC application that allows the user instant access to the Google Maps. The map shall display a small marker representing the GPS coordinates or GSM cell at a certain time of the day. B. Application architecture Data from the application settings are saved in a XML file, and contacts are stored in the PDA memory by the Microsoft Outlook. The GPS coordinates and GSM cell are separately stored in text files. To improve security the password is saved in a hidden file. When the application is started, the data is loaded from the XML file and will apply it to behave according to those parameters. Each SIM card is identified by its Integrated Circuit Card ID (ICC-ID). ICC-IDs are stored in the SIM cards and are also engraved or printed on the SIM card body during a process called personalization. When started the application can detect the ICC-ID of the current SIM card and compare it to the predefined ICC-ID to detect unauthorized SIM card in the device. [10] To compare the obtained GPS coordinates with the predefined interest point, we have selected as reference the ellipsoid world geodetic system rev. 1984 (WGS 84) [11- 15]. WGS84 is a global datum used by the United States Global Positioning System. The datum is currently defined by the coordinates and velocities of 18 GPS tracking stations maintained by the US Air Force (USAF) and US National
Geospatial Intelligence Agency (NGA). To better understand the user interaction with mTracker, the corresponding UML diagram is shown in Figure 2.
Figure 2. mTracker UML diagram.
The application architecture and its working principle are centered on the use of GPS and GSM Cell ID. These are the most common technologies for these kinds of applications. Other possible approaches may include a combination of other LBs like wireless hot spots or via Bluetooth. Crossing data from all the LBs should provide much more accurate position of the device. Furthermore, unlike the GPS, the GSM cell ID, wireless hot spots and tracking via Bluetooth are able to get the device position even they locate indoors. After installing the application on the PDA, it will be set to start running in background every time the device operating system restarts. This will ensure that those who do not have the password can change the application settings like the activation/deactivation of both tracking tool and SIM card detection tool. If the administrator has activated both tools, they will start to execute automatically when the device is restarted. C. Technologies The mobile application targets Pocket PCs running Windows Mobile 6.0 (wm6). We have decided to develop the application under the .NET Compact Framework from