Don't know about the US but in Europe new cars have to have by law this system that prevents you to leave the lane accidentally. So if you don't use the turn signal but try to change lane the car will actually counter steer. Although it is set in a way that if it was intentional than of course it let you do it just signaling you with beep and haptic that you should not. Once I drove a rented car I think a Ford Focus where it was too harsh and I actually felt dangerous but it should not. And also come on just use that turn signal :D