[bluGill]

My car has that - there are too many false positives for it to be useful. I most commonly hear get the warning when there are two left turn lanes and I'm in the right one (because I need to turn right at the next road). Sure there is a car to my left, if it doesn't turn left I'll hit it, but the other car would be at fault in that case.

I will admit that there have been a couple times it saw the car I was about to merge into before I did. It is not clear if I would have seen the car a moment latter anyway or not.

[mikeash]

Mine has never had a false positive. I've yet to accidentally merge into anybody with it, so I don't know how it behaves in the situation it's supposed to handle.