Abstract
Smartphones and tablets are getting more accessible to the common people with affordable price and wide selection of hardware specifications. Most of the mobile devices come with built-in cameras, microphones and GPS sensors that can be used as surveillance device. We propose a location tracking system that would track and send user's geographical coordinates stealthily in the background using multiple missed calls to a predefined phone number. The receiver would decode the location data using an agreed format of the duration of the missed calls. Delay in the internal message passing of Android and the latency of mobile cellular network base stations reduces the bandwidth that can be achieved by our prototype and also causes errors. There are cases where duration of a missed call is mis-categorized into unintended group. The grouping is used for coding of location data. We are able to send data up to 0.12bit/s with a modified phone application on Android operating system. The location of the user can be transmitted in 5 minutes. Subsequent location notification costs less time as only the changes in coordinates compare to previous update are sent. The proposed method of data transmission using missed calls can be easily replaced by internet connection or Short Message Service(SMS) but typically it would cost money to do so. Further fine-tuning of the missed call duration parameter should increase the bandwidth of the system. Inclusion of data detection or correction code should reduce the interpretation errors.