You don't get privacy in MY house. you want "privacy", that happens when you move out, otherwise deal with it.
Now... Having said that, when each of my kids turned 18, they were afforded a degree of privacy. I could pop onto any of my kids PC's by remote and observe what they were doing, but at 18, I stop doing that. Until they were 18, they had to turn in their phones at 9pm sharp. We had a spot for all of their phones to be deposited at night. Also, the kids were not allowed to have social media of any type until 18 and I would routinely audit their PC's and phones until they hit that age.
My wife would go through their rooms until she physically couldn't anymore. Then I did it. Diaries were off limits but pretty much everything else was fair game.
You're supposed to guide and protect your child. In order to do that you need to know what they're up to, so then there's no such a thing as "privacy" in your home. You know what they're doing and who they're with. That's life, especially in this day and age. You instill values in your children, but that needs to be audited periodically in order to make sure you kids are on the straight and narrow.
Now... having said that, you could wind up with a mischievous, smart ass of a kid like me, that knew his moms was going through his shit from time to time and would do stuff like cooking up salt or sugar crystals after school and bagging it up, taking powdered sugar and rolling it into ziploc bags, and mixing oregano and burnt leaves from the back yard into ziploc bags to make it appear as if I'm a drug dealer. Let her find it hidden very well in my closet, gettin yelled at and cussed out over it until I told her to "taste it" and having moms realize I played her so she wouldn't pull that shit again anytime soon.