For those who dont know the function of REST button....
Residual heat mode
The heat which is stored in
the engine is utilized for
heating the interior when the engine has
been switched off (while waiting at a
railroad crossing, for instance). In ignition
key position 1, you can alter the
settings of the automatic climate control.
In ignition key position 0, the system
automatically directs heated air to
the windshield, side windows and footwells. <<< BMW Owners manual
NOTE: It only works on temperatures equal or lower than <= 10ºC /
50ºF (Outside Air Temperature)