A periodic on-screen reminder showing how long you have been playing and often what you have won or lost, which interrupts the session and requires you to acknowledge it before continuing.
What it does
At an interval you choose, commonly 15, 30 or 60 minutes, the game pauses and a message tells you how long you have been playing. Most implementations also show your net position for the session, and you have to click to continue or to stop.
Why it works at all
Slot play is designed to compress the sense of time passing: no clocks, continuous audio, fast rounds, no natural stopping point. Two hours can genuinely feel like twenty minutes. The reality check reintroduces the clock.
The interruption is the mechanism, not the information. Being forced to make an active choice to continue is different from drifting into continuing, and that small friction is what changes behaviour.
Setting one that is actually useful
Thirty minutes is a reasonable default. Fifteen is better if you are trying to cut back and can tolerate the interruption. Anything over an hour is long enough that the session has already established its own momentum.
Some operators default to no reality check at all, so it may need switching on. In the UK, reality checks are a licence requirement rather than an optional extra.
What it is not
It is not a limit. It tells you where you are and lets you carry on. If you find yourself acknowledging reality checks and continuing every time, the check has done its job by giving you the information, and the next tool up the ladder is a deposit or loss limit rather than a shorter reminder interval.