ADAS (Advanced Driver Assistant System) is a system on some dashcams that alarms the driver in certain critical situations. It keeps an eye on the road in case the driver seems to have lost attention. ADAS usually consists of the following functions that can be turned on and off separately. 

FCWS: Forward Collision Warning System. This system gives a warning when a vehicle in front is approached at high speed, for example in a traffic jam. The dashcam uses different visual sensors and GPS data to determine whether the situation is critical and should give a warning.
LDWS: Lane Departure Warning System. This system gives a warning when the car is about to leave the current lane slowly and unnoticed.
FVSA: Forward Vehicle Start Alarm. This system warns the driver when the vehicle in front is driving away but the driver's car remains stationary. 

Some ADAS systems can give addition warnings, like a Fatigue alert on Mio dashcams when the person has been driving uninterrupted for a long time and it's probably a good idea to take a brake.

Note that above systems work best in light and clear environments and depend heavily on road conditions. LCWS and LDWS only work on +60km/h and on straight A-roads.