problem with door unlock when cold

Hi, I have a problem with door unlock when weather is cold. Car is Ford Focus 2001, European model. I've put in alarm system and was working ok, but after some time it started to act strangely, when there's cold weather (around 0 degrees) then after pushing unlock button on remote, doors unlock and then locks up again right away. I've tried unlocking with button on Ford key and it works ok, unlocks and doesn't lock up. Any advice, what could be wrong? Strange thing is that during summer when it's warm, door unlocks without problem...

Thanks!

I was hoping the relevant experts would reply, but I was wondering of it could be you battery?

Maybe it's old?
And battery voltages drop with colder temperature, hence maybe affecting the modules sensing circuit.
Or similar if the cold means stiffer solenoids etc - a voltage dip that causes module problems.

Your car may have a lock position sense wire. Basically, the wire will go to and stay at ground when the doors are locked. If you manually lock the driver's door, do the other doors follow? If yes, the actuator in the driver's door may be failing and not unlocking the door all the way(far enough to stop ground on the position sense wire) and the car thinks someone is manually locking the door then activating all the actuators and re-locking the doors. How's that???

Doesn't explain how it works with the factory fob but still may be something to look at.