I used to work for the railway and for many years, (mainly shift-work, as I used to drive trains). Each winter, I would get up at some ungodly hour (earliest start was 0320hrs. with a 40 minute drive to get to work at 0420hrs.) When I was ready to depart, I would start the car and scrape the front and side windows, then depart.
As I got older I started to get lazy: I would get both sets of keys, start the car with one set and use the second to lock the car and return indoors. Returning later to a warm and defrosted car.

So, the other a.m. my car was frosted, so I used one fob to start the car, got out and tried to lock the car with the other. It wouldn't lock the car with a fob already in.

Now ,before anyone starts on about global warming etc. etc. The total amount that humankind contribute to global warming is approx. 0.02%. (Take water vapour out of the equation)

Has anyone else tried this and/or am I missing something?