What city are you in? Backflow preventers are required in cities that use culinary water for the sprinkler supply line. If your city has secondary water you will have a filter most likely. There should always be a shut off valve of some sort. It could be close to the meter. Some houses with new construction have a valve for the sprinklers inside the home by the shutoff for the house and then the line goes back outside. Some house have them close to the house where the main line enters the home.