1. A method comprising: receiving, at a mobile device, a location of an entity socially connected to a user associated with the mobile device, the entity and the user socially connected through an on-line social network with which the user and the entity are associated; determining, by one or more processors of a geographic-positioning component of the mobile device, on a periodic basis, a current location of the mobile device; determining, by the processors of the geographic-positioning component, whether the current location is within a geographic region defined at least in part by the location of the entity; and if the current location is within the geographic region, then transmitting, by the processors of the geographic-positioning component, a message to one or more other processors of the mobile device, the message causing one or more of the other processors to transition from a sleep state to an active state.