https://www.cnn.com/travel/article/colorado-lost-hiker-phone-trnd/index.html [cnn.com]
"One notable take-away is that the subject ignored repeated phone calls from us because they didn't recognize the number," LCSAR (Lake County Search and Rescue) wrote. "If you're overdue according to your itinerary, and you start getting repeated calls from an unknown number, please answer the phone; it may be a SAR team trying to confirm you're safe!"
Umm, ok, but why not leave a message if the callee doesn't answer? :)