We always check that all 8 paws are visible when we leave the house. It happens that you just get startled: "I haven't seen Filou for some time." and then we usually go into major search mode because we are sure either he snuck in a closet etc. or he made himself invisble to run in the cellar (Of course he knows purrfectly how to become invisble ).

We do that several times a day and most of the time he's just somewhere- but at some times we are really glad we checked.