A major concern for today's smartphones is their much faster battery drain than traditional feature phones. The difference is mainly contributed by those more powerful but also much more power-consuming smartphone components, such as the multi-core application processor and the high-definition (HD) display. In this paper, we investigate how to increase the battery life of smartphones by minimizing the use of application processor and HD display for operations related to basic functions. We find that the application processor is often waken up by a process running on it, called the Radio Interface Layer Daemon (RILD), which interfaces users/apps to the GSM/LTE cellular network. Consequently, we design a Smart On Demand (SOD) configuration that reduces the smartphone energy consumption by running RILD on a secondary low-power microcontroller and by using a secondary low-power display to interface the user with basic functions. Thus, basic phone functions are handled at much lower energy costs while the power-consuming application processor and HD display are waken up only when one needs to use smart apps. We have built a prototype of SOD and evaluated it with real user traces. Our results show that SOD can increase its battery life by up to 2.5 more days.