I have to admit I was a bit stupid and thought the start button came with the S5 and was pretty dissapointed when I collected my car and found out it wasn't there. With hindsight I'd have to say if you can afford the keyless entry get it, I wish I had and it would seem I can't have it retro fitted either. I will also add that the key into the slot in the dash has "stuck" a couple of times forcing me to start the car several times before I could retrieve my key from the slot and lock the car. Bottom line keyless entry is the way forward, take it from someone who now gets to regret not spec'ing it.