Activities of prominent terrorist groups like Boko Haram, Al-Shabaab, Ansaru, and Ansar Dine have left thousands of people dead and properties destroyed for a number of decades in some developing nations. The high level of insecurity occasioned by operations of terror groups has impacted negatively on the socio-economic development of these nations. On the other hand, the use of mobile devices, such as cell phones, has gained prominence in developing nations over the past two decades. Putting side-by-side these two facts, namely, that the menace of terrorism among some developing nations is alarming and that the use of mobile devices is common among citizens of developing countries, this chapter develops a mobile application prototype called TerrorWatch. TerrorWatch is equipped with relevant menus, buttons, and interfaces that will guide a user on what to do when confronted with a terrorist attack or threat. The unified modeling language (UML) was deployed to design the architecture of the application, while the object-oriented paradigm served in the implementation.