A reality check is a timed pop-up that interrupts play at an interval you choose — every 30 or 60 minutes, say — to state how long the session has run and, on many sites, your net position. You have to click to continue, which breaks the automatic flow of spin-after-spin.
Why the interruption is the point
Slot and live play are designed to be frictionless and to distort your sense of time. A reality check reintroduces friction on purpose. It does not stop you playing; it makes you decide, consciously, to carry on, which is exactly the moment good design tries to remove.
What the British rules actually require
Reality checks are not a courtesy in Great Britain; they are a licence condition. The Gambling Commission's remote technical standards require every online operator to offer them, to show how long the session has run when one fires, and to make the customer acknowledge it before play continues. Since the slot-design rules of October 2021, slots must also display the session's elapsed time and net position on screen throughout play, alongside a minimum spin speed and no autoplay — so the reminder is now the interruption on top of a display that is always there.
The gap is the default. Most operators ship the interval at 60 minutes, and an hour of slot play at two and a half seconds a spin is well over a thousand spins. Fifteen or twenty minutes is an interval that arrives while a decision is still yours to make.
Using it well
Set the interval short enough to matter and pair it with a deposit limit and, if you need it, a self-exclusion. If you find yourself clicking through the reminder without reading it, that reaction is itself information worth taking seriously: the free help signposted under problem gambling is there for exactly that.