not a problem for me this year as I now work nights (though 1 time last year it was frozen when I tried to come home!) but before I used to leave for work I'd boil the kettle and pour a bit over the lock
couple of times I couldnt even get my key in the lock, poured water over it, then by the time I got to work it was re-frozen and I couldnt lock up grrrrr
Get remote locking
can get universal kits for around £20 and easy to install