Is there an app that will report on devices that have not reported in or shown signs of activity for a certain time?
Try "Simple Device Viewer"
name: "Simple Device Viewer",
namespace: "krlaframboise",
author: "Kevin LaFramboise",
description: "Provides information about the state of the specified devices.",
category: "My Apps",
iconUrl: "https://raw.githubusercontent.com/krlaframboise/Resources/master/simple-device-viewer/simple-device-viewer-icon.png",
iconX2Url: "https://raw.githubusercontent.com/krlaframboise/Resources/master/simple-device-viewer/simple-device-viewer-icon-2x.png",
iconX3Url: "https://raw.githubusercontent.com/krlaframboise/Resources/master/simple-device-viewer/simple-device-viewer-icon-3x.png")