so my question?
https://www.securitywarehouse.co.uk/catalog/honeywell-dt8012f5-dual-tec-motion-sensor-with-petimmunity-p-4033.html
https://www.securitywarehouse.co.uk/catalog/knight-grade-3-4-terminal-surface-contact-p-2558.html
GSM unit
https://www.securitywarehouse.co.uk/catalog/menvier-gsm-speech-dialler-p-2989.html
I would suggect pro monitoring not diallers as the path is not monitored using a dialler. Something like a webway unit or dualcom etc
The only way to achieve stanby of that time would be with large batteries and some sort of split charge system. Even the big Vanderbilt VDS Unit wont take a battery big enough.
YOu would need to calculate or measure your standby current, size the batteries and chargers as required and connect the to the panel via a relay in the event of an ac failure.
Your batteries will have drastically reduced capacity in those tempratures and is outside the manufactures specs for devices. YOu may need small heaters (resistors) in the devices if the cold was a problem, but that will use a lot of power.