If you want to keep your chickens for more than a few nights that door needs to be shut and locked every night. No area is free of predators that will dine on your chickens. Suburban areas have plenty of coons and possums.
There are folks that have built Fort Knox chickens runs that will keep predators out so they don't have to lock the chicken door but it is expensive to do so and time consuming to complete. If you go this route your can find post here telling you how to do so.
If I am leaving for the evening and I won't be home before dark I run the chickens in and lock up. Learned that lesson the hard way.
I play softball one night a week and generally don't get home until 10:30 or 11:00 at night. For years I got a way with only locking up after I got home. Well one night I go out to lock up and the coon beat me to the chickens. He killed 10 of my 20 hens. I got even though. I locked the chicken door before he could get out and went and retrieved by .22.
This is the one area of chicken keeping you must be vigilant about. The night you forget or that cold rainy night you don't feel like going out and don't will be the night the coon finds your birds. Remember the coon checks each night to see if you completed your chores.