Most of the smartphone CPU has multiple speed stages. Take Samsung Galaxy S II as example. It has 6 stages ranging from 1.2 GHz, 1 GHz, 800 MHz, 500 MHz, 200 MHz and deep sleep mode. Do you know which speed stage does your Android phone uses the most? If no, CPU Spy for Android is the application that will tell you. CPU Spy displays the time of the CPU spends in each frequency state. It is a useful tool to diagnose battery problems. And understand it better to tweak by overclock / underclock and undervolt.