Yes, good idea to put an old blanket over the backflow preventer. It's usually on the side of your house. About 4 years ago, we had a freeze and water got under the plastic cap of the backflow preventer. The water expanded and turned to ice, breaking the cap. It was like a geyser with all the water shooting out of the line. This happened to about 40 homes in Summerhill. Now, everyone puts a blanket over it.Our backflow preventer looks something like this.Seems like, from the article, they may have replaced these with a black box on the side of the house.
irrigation backflow preventer - Yahoo Search Results