its called the " stop start system"
thanks to the eu and their obsession with regulation in the name of improving the environment, it is mandatory on all cars sold in the eu and in the uk now.
it increases the complexity of the engine management systems and their various components and hence the cost of cars, their maintenance and parts replacements with very little benefit to the environment. i used it for the first year i had the car and after the info system on the car informed me i had saved less than 500cc of petrol i de activated the system. it is a very annoying feature anyway, and does not operate if the air con, the heater, the heated seats, the steering wheel heater or the lights are on.
Start-stop system - Wikipedia