The SO gave his father and iPod years ago and later an iPad. When his dad started developing dementia and constantly misplacing items, we loaded the tracking feature on on my iPad. One time, he was staying with us, and between the previous evening and the next morning, the iPod was missing.
Dad never left the house. Since his brother and SIL had been there the night before, we checked with them to see if they had seen it, used the tracking app to no avail, and then started meticulously checking everywhere in the house. This was several years ago, and we still do the occasional search including the tracker app.
My guess is that it was either switched off or the battery was dead when it went MIA. Since he is known to squirrel items away at night after a glass of wine or two, it’s likely that it will still turn up in a pocket or in some nook that escaped our search.
In order to make sure the app worked, we tested it with his iPad, which we also set up to track. If I recall correctly, it did. Otherwise, I would have deleted the app.