US Patent 9520045 Establishment and detection of breakage of wireless leash between devices

Companion and accessory devices can be wirelessly leashed together in a manner that enables the devices to estimate their proximities to each other. One device can periodically attempt to detect a signal from the other device. For each attempt, the attempting device can store an indication of whether the signal was detected. If a number of times that the signal was undetected exceeds a threshold, then the attempting device can perform specified operations, such as alerting a user that the wireless leash was broken. As another example, one device can detect that a strength of a signal from the other device exceeds a threshold. In response, the detecting device can measure signal strengths more frequently. If the measuring device then detects that the signal strength exceeds another threshold, then the measuring device can cause specified operations to be performed, such as data synchronization between the devices or unlocking a device.