1. A computer-implemented method, the method comprising: receiving, by a mobile device, an input associating a geographic area with an application program, the input specifying that the application program shall be invoked when the mobile device enters the geographic area, wherein the application program is configured to execute in an application subsystem of the mobile device, the application subsystem comprising an application processor; submitting, by the mobile device and to a server, a request for information on monitoring whether the mobile device has entered the user-defined geographic area; receiving, by the mobile device and from the server, an identifier of a wireless access gateway, the identifier being associated with the geographic area; registering, by the mobile device, the identifier of the wireless access gateway to a baseband subsystem of the mobile device, the baseband subsystem having a baseband processor that consumes less power than the application processor when the application subsystem is activated; monitoring, by the baseband subsystem of the mobile device while the application subsystem is in a power-saving operation mode, a wireless signal received by the mobile device, including determining that the wireless signal is associated with the registered identifier of the wireless access gateway; notifying, by the baseband subsystem, the application subsystem of the mobile device that the mobile device has entered the geographic area; and in response, activating the application subsystem and executing the application program by the application subsystem.