Motion sensors have 3 position adjustment. Switch under the battery.
Of course you can add sensors and just cover all your windows and doors and not use motions.
I am in my second house and 4th year with Simplisafe. I like it a lot.
If you've ever moved with an alarm you know it sucks.
With simplisafe I had the new house set up the first night we lived here. Some double stick foam tape and 'command' refills and that's that.
As for sensors falling off in cold, hasn't happened to me on my garage doors or any doors for that matter.