Yes, it brakes if the driver does nothing. Preferably slowly if the distance to obstacle allows it. If the user brakes instead, the human operator takes over, even if s/he softly brakes for n seconds, it could turn off the hazard warning. If there isn't sufficient time to warn the driver, have it just brake automatically to avoid collision. This is what AEBS/AEB collision avoidance systems do. Frequency of beeping could be increasing with distance to object, just like parking sensors. Continuous beep = accident imminent.