In one embodiment, a method includes receiving, at a mobile device, information on one or more entities socially connected to a user, the information including a location for each of the entities and an affinity score; determining on a periodic basis, by one or more processors of a geographic-positioning component of the mobile device, a current location of the mobile device; determining, for each of one or more of the entities, a radius from the location of the entity based at least in part on the affinity score for the entity; determining whether the current location is within an area defined by one of the radii; and, if so, then transmitting by the processors of the geographic-positioning component a message to one or more other processors of the mobile device, causing one or more of the other processors to transition from a sleep state to an active state.