It monitors driver behaviour closely - noting any erratic steering wheel movements and lane deviations, for example - so it can judge the moment that you are starting to feel sleepy and need to stop. It also continually evaluates traffic signals on the road when you are driving at speeds of more than 60km/h. and works out when it's time to take a break.
If the system detects that you're starting to lose concentration it will alert you with a visual display on the dashboard and a warning sound. If you haven't taken a break within 15 minutes, the system will repeat the warning.
So it's always up to you to plan rest breaks into your journeys, of course, but you'll find our Driver Alert System a helpful aid to safer driving.