Dynamic duty-cycling of processor of mobile device based on operating condition of mobile device

1. A method comprising:

recording a first location of a mobile device;

determining, by one or more processors of a geographic-positioning component of the mobile device, on a periodic basis, a trajectory of the mobile device, wherein the trajectory is calculated based on present and past user locations;

determining, by the processors of the geographic-positioning component, whether the trajectory is outside a geographic region defined at least in part by the first location and a radius, wherein the radius is adjusted from a pre-determined value based on:

a detected velocity of the mobile device;

time of day information;

a battery level of the mobile device; or

an error of the first location measurement or the trajectory measurement; and

if the trajectory is outside the geographic region, then sending, 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.

2. The method of claim 1 , wherein the message identifies the trajectory.

3. The method of claim 1 , wherein the first location is based at least in part on:

a global positioning system (GPS) signal;

a Wi-Fi signal; or

a cellular radio signal.

4. The method of claim 1 , wherein the first location or the trajectory is based at least in part on user-submitted location data.

5. The method of claim 4 , wherein the user-submitted location data comprises social-networking information submitted by using social-networking functionality.

6. One or more computer-readable non-transitory storage media embodying software that is operable when executed by one or more processors to:

record a first location of a mobile device;

determine, by one or more processors of a geographic-positioning component of the mobile device, on a periodic basis, a trajectory of the mobile device, wherein the trajectory is calculated based on present and past user locations;

determine, by the processors of the geographic-positioning component, whether the trajectory is outside a geographic region defined at least in part by the first location and a radius, wherein the radius is adjusted from a pre-determined value based on:

a detected velocity of the mobile device;

time of day information;

a battery level of the mobile device; or

an error of the first location measurement or the trajectory measurement; and

if the trajectory is outside the geographic region, then send, 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.

7. The media of claim 6 , wherein the message identifies the trajectory.

8. The media of claim 6 , wherein the first location or the trajectory is based at least in part on user-submitted location data.

9. The media of claim 8 , wherein the user-submitted location data comprises social-networking information submitted by using social-networking functionality.

10. A mobile device comprising:

one or more processors; and

a memory coupled to the processors comprising instructions executable by the processors, the processors being operable when executing the instructions to:

record a first location of the mobile device;

determine, by one or more processors of a geographic-positioning component of the mobile device, on a periodic basis, a trajectory of the mobile device, wherein the trajectory is calculated based on present and past user locations;

determine, by the processors of the geographic-positioning component, whether the trajectory is outside a geographic region defined at least in part by the first location and a radius, wherein the radius is adjusted from a pre-determined value based on:

a detected velocity of the mobile device;

time of day information;

a battery level of the mobile device; or

an error of the first location measurement or the trajectory measurement; and

if the trajectory is outside the geographic region, then send, 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.

11. The mobile device of claim 10 , wherein the message identifies the trajectory.

12. The mobile device of claim 10 , wherein the first location or the trajectory is based at least in part on user-submitted location data.

13. The mobile device of claim 12 , wherein the user-submitted location data comprises social-networking information submitted by using social-networking functionality.

14. The method of claim 1 , wherein:

the geographic region is further defined by one or more entities of a social-networking system;

a user of the mobile device is a user of the social-networking system; and

the user is associated with one or more entities through the social-networking system.

15. The method of claim 14 , wherein the one or more entities comprise geographic locations associated with the user.

16. The method of claim 14 , wherein the one or more entities comprise another user of the social-networking system.

17. The media of claim 6 , wherein:

the geographic region is further defined by one or more entities of a social-networking system;

a user of the mobile device is a user of the social-networking system; and

the user is associated with one or more entities through the social-networking system.

18. The media of claim 17 , wherein the one or more entities comprise:

geographic regions associated with the user; or

another user of the social-networking system.

19. The device of claim 10 , wherein:

the geographic region is further defined by one or more entities of a social-networking system;

a user of the mobile device is a user of the social-networking system; and

the user is associated with one or more entities through the social-networking system.

20. The device of claim 19 , wherein the one or more entities comprise:

geographic regions associated with the user; or

another user of the social-networking system.