New System for Unheated Building in Wisconsin, Will it Work

@Dman1959 unless you are a gambling man, you are best to move on. The manufacturer specs are not going to cut 0 degrees and  your warranty will be void. Yes, I do have a motion and an entry sensor in my garage, and it has been to single digits here near Chicago but doubt the base or keypad would survive.

@Captain11, Aren't the keypads usually mounted outside? There must be other systems in the Cold Northern states.  Also I could put the base in a small heated box inside the building if the rest of the system sensors can take the cold.  I am in central Wisconsin so it isn't to much colder than Chicago. Does Simplisafe specify the minimum temperature of all their components for 0 degF?

The keypads are designed only for the interior of a home/structure (and only the video doorbell is designed for outdoor use - the simplicam used with the separate camera cover, and the external siren could be used outdoors in warmer weather, but they still need protection from hot sun and snow/ice/rain such as under an eave, porch, etc) . I'm not sure you'd want to put the base station in a "small heated box", as it could compromise the base station if the box was too warm or hot.

Call SS and ask them about the temp ranges for the sensors, make sure you tell them which system you're interested in (SS2 vs SS3).  As Captain noted, you wouldn't be able to count on a warranty under the conditions you're thinking of, not to mention the battery drain on nearly all of the components.  Only way to know for sure though, you could try it, and if it didn't work, return during the 60-day return policy (btw, the 60-day return policy starts on the DATE OF PURCHASE - so take into account at least a week or more for the system to even get to you after ordering - warning: during the holidays, getting a system or support is absolute mayhem).