The short answer is yes, for most cats, on a modern box with three or more independent safety systems. The longer answer involves kittens, very small adults, and the specific circumstances in which sensors miss a cat. This page covers both, without either the marketing gloss or the horror stories.
How the safety systems actually work
Weight sensing. The unit knows a cat has entered because the load on the base changed, and it will not start a cycle while that load is present. This is the primary system on nearly every box and it is why a level floor matters so much.
Infrared or laser entry detection. A beam across the entrance detects a body crossing it. This catches cats the weight sensor might miss — a very light cat, or one perched at the entrance without committing weight to the base.
Anti-pinch reverse. If the mechanism meets resistance mid-cycle, it stops and backs off. This is the last line of defence, and it is the one specification we would not buy a box without.
Where they fail
Cats under about 3 lb. Most weight sensors have a minimum threshold, typically 3 to 5 lb, below which a cat may not register. Kittens are genuinely at risk on boxes without independent entry detection, and no manufacturer recommends these boxes for kittens under four months.
Uneven floors. A tilted base gives unreliable weight readings, and unreliable weight readings are the most common root cause of a safety system behaving unexpectedly. Level the unit and re-tare it after every litter change.
A cat that enters at the wrong moment. Some cats will step in during the delay countdown. On a good box the cycle stops or reverses. On a box with two systems instead of three, it stops.
Which cats need more caution
Kittens under four months, or any cat under 3 lb. Use a conventional tray until they are over the weight threshold with margin.
Very large cats. Not a safety risk so much as a fit risk — a cat that cannot turn around comfortably will stop using the box, and a cat over the stated maximum may trigger error states.
Cats that sleep in the box. Uncommon but not rare, and it is the scenario the delay timer exists for. Lengthen it if your cat does this.
What to change on day one
Level the unit properly. Use a phone level on the base, not your eye on the floor.
Lengthen the cycle delay. The default on most boxes is seven minutes; fifteen costs you nothing and removes most of the scenarios in which a cat returns mid-cycle.
Run one cycle with the unit empty and watch it. Understanding what a normal cycle looks and sounds like is how you notice an abnormal one.
Leave the old box in place for two weeks. Cats need an alternative while they decide, and a cat that is forced into an unfamiliar box is a cat that will find somewhere else to go.
How we test this
We introduce a weighted, cat-sized test object at five points in the rotation, at 3 lb, 8 lb and 18 lb, and record whether the unit stops, reverses or continues, and how long it takes.
We never test safety systems on a live cat. Every safety number on this site comes from a test object.
A box that continues at any weight at any point in the cycle cannot score above 5 on safety, regardless of what else it does well.
The short version
Three independent safety systems, a level floor and a longer delay timer covers almost every real-world risk. Kittens under 3 lb should not use one at all.