Which parts are needed for ACS to work ?

Cam, radar,sensor, Laser beam? ??

From NCAP report-

http://www.euroncap.com/en/ratings-rewards/euro-ncap-advanced-rewards/2011-ford-active-city-stop/

'Ford Active City Stop is a system which helps to avoid or to mitigate accidents at low speeds. At speeds up to 30km/h, a lidar (Light Detection And Ranging) sensor positioned at the top of the windscreen scans the area up to around 7.6m ahead of the vehicle for possible obstacles. If the vehicle detects a braking, slower-moving or stationary vehicle in front and it determines that a collision is likely, the brakes are pre-charged. If the driver remains inactive (no steering or braking input), the car applies the brakes automatically and reduces engine torque.
At relative speed differences less than 15 km/h then Active CityStop may help the driver to entirely avoid the collision with the obstacle in front. If the relative speed difference between the two vehicles is between 15 and 30 km/h the impact is unavoidable through braking alone but Active City Stop will aim to reduce speed prior to the impact.
If the driver intervenes to try to avoid the accident, either by accelerating hard or by steering , Active City Stop will deactivate. Active City Stop is unusual for an autonomous emergency braking system in that it does not give the driver a warning of the impending collision, and brakes very hard, very late. This is intentional: the way in which the system intervenes is not comfortable and drivers will not become reliant on it to avoid around-town accidents'

Sent from my SM-G930F