Techniques for location source control for paired devices are described. Location source control selects a location source for a mobile device. The mobile device can receive, from an application program, a request for determining a location of the mobile device. The mobile device can determine a first location estimate using a location subsystem of the mobile device. The mobile device can determine whether to provide the first location estimate as input to the application program, or to provide a second location estimate as input to the application program. The second location estimate can be an estimated location of the companion device and determined by the companion device.