Charmion wrote: ...any safety measure should be automatic...

A good principle. I was taught that on a 'defensive driving' course once. (My employer was taken over by a US oil services company who were - creditably - very safety conscious and they made it a condition of having a company car.) If you only indicate when you think someone will be affected, you may be wrong.

My last couple of cars (that covers 15 years) had a feature whereby if you started signalling left, say, to change lanes, and aborted the move, you couldn't cancel the signal before 3 flashes - except by signalling right. I think this is dangerous: you can alarm the driver into whose lane you intended to move by continuing to signal, or the driver who is overtaking you. I always disable this feature.