Having multiple "check in" points, can also give direction of travel and speed. Knowing this, you could possibly extrapolate the general health of the individual at the last known location. Combining this information with knowledge of the person being sought, the current weather conditions, and the terrain, a general idea of the possible intended path and current location can be determined. This will allow searchers to focus on areas that would have a higher likelyhood of having a missing and/or injured person. If the only way to keep going east was along a ledge, check the bottom of the ledge. If there is a flowing stream near a trail, check along the stream ( or downstream ).

It would be nice if the PLB's allowed for a "non-emergency position update". Something like double-click a button, that sends a signal which is recorded as a route start/end. It could give periodic updates (maybe once every 15 minutes ), but allow manual update by pressing the button once. Software on the end could give warning alerts that a device hasn't given an update after 2 times the periodic interval. Not an end-all solution, and there could be false alarms (what if the battery dies?), but it would take care of the "I cannot reach the PLB" situation.