Reset timers application note from Fairchild Semiconductors. Link here (PDF)
As smart phones continually add functionality, it increases the likelihood of device lock up. This condition has been called the “White Screen of Death” which is a new take on the popular phrase used to describe Windows PCs after a system fault. Before the advent of standalone reset timers, users were required to remove the phone battery to force a device restart. As more device suppliers remove access to the device battery, it has become necessary to provide a more convenient way of forcing a device reset.
Reset timers create a failsafe mechanism for users to reset the phone using a single- or multiple-button long key press. Reset timers have an advantage over software solutions in that the independent, hardware-based solution is not susceptible to software crashes. The need for hardware-based reset timers is the result of an increased likelihood that device operating systems can be derailed by the growing applications and features they must support.