Remote start is the answer - shame it's not legal here. I used to use it in the US when it was cold (or indeed hot, with A/C). Start the engine from inside the house without unlocking the car.
Current: 2013 F10 520d M-Sport, Professional Media, Visibility Pack, Reversing Camera, DAB
Previous: 2011 F10 520d M-Sport, 2008 320i M-Sport Coupe, 2002 325i, 2001 318i valvetronic, 1998 318i, 1996 525i, 1990 Porsche 944S2