One of our cats (we had 4 at the time - all indoor critters) pulled a major disappearing act, for about 8 hours, to the point where I was certain he had somehow gotten out of the house and likely been picked off by a car. I had looked everywhere, tried the laser pointer, jingle toys, treats, food - nothing. I was so distraught I couldn't even eat dinner.
It was bitter cold. Twice, I went walking around the neighborhood, calling for him. The second time, it was dark, and there I am, looking for a black-and-brown tabby cat in the dark. Good luck with that, right?
I came back in the house, to find our younger son coming down the stairs with the cat in his arms, saying, "Well, well well - look who showed up." I was so relieved I cried.
The cat had been under our younger son's bed, where I had looked more than once. I had not looked well enough. It's a platform bed, with storage drawers, and the cat had crawled all the way up against the headboard, into a space next to a drawer that you could not see into unless you took the mattress all the way off the bed, which I had not done.
Our 2 current cats wear TILE trackers on their collars. Winston, the "lost" cat, had one at the time of this story, but the battery had run out and I had not replaced it. A lesson learned. Any day I haven't seen either of them for a while, I go around the house "beeping" them for my peace of mind.