Running additional AC power to those same phones can be cost prohibitive. Five of the six phones run off of telephone power alone, while the sixth phone requires not only AC voltage but also a four-hour battery backup. With the additional cost of running AC lines and changing batteries, this seems like a poor option, especially when there are so many line-powered phones available. A chill wind. Security practitioners should consider operational temperature ranges when purchasing an emergency phone, especially if the phones will be placed in cold climates.
Some manufacturers offer phones specifically made for subzero conditions.
To move those pesky electrons at that temperature, the phones incorporate heaters, which are usually AC powered. Other phones specifically stated that they were for indoor use only. Weather resistance should also be a consideration. They also include a speaker with a plastic cone instead of the traditional paper cone to protect it from the elements. Only four of the phones researched for this article claimed to be weather resistant.