The above answers I think answer your question. However, to expand, the handbrake will release when you apply some power with the engine, but not unless this is done. FYI, this also happens with the regular hand-brake (switch), which I didn't realise until I got my car... As a result, I rarely use the assist, because I just pull the handbrake when I stop... However if you are stop-start on a hill, such as on a steep, busy slip-road or T-junction, then it's great... although works best if you stop the car on the brake and not let the car roll to a stop under gravity... which is a habbit of mine! Here, it can be a little slow applying and the car rolls back a few inches and makes a 'creaking sound' from the discs whilst it stops the car!