One of the beauties of Onstar with the GM stuff. Just get on your smart phone and tell it to start the vehicle. It will run for 5 minutes. All locked and secured. I have tried it to see how well it works, and it does work well. But my vehicles all reside in heated garage, so I have no real need to do any of this. I have used the feature, maybe, twice when we went to someone else's place and were there for several hours during cold weather. Before we got ready to leave, remote started the vehicle via the smart phone app.
Another great way to deal with diesel warm up is to get a Webasto or Espar fuel fired coolant heater. Set it on a timer to operate about an hour before you get ready to use the vehicle and it will fire up, using the vehicle fuel system, and have the engine up to 140F in short order. They even have gasoline fired ones for gasoline engine use. Use very little battery and only consume, maybe 1/8 gallon of fuel per hour.