Forget To Lock

I see my father has changed the 4 old doorknobs that we used to have in this house. All four are new but I think the two doorknobs in our main doors wouldn't give them much security because when my brother goes out the house, he wouldn't bother locking the doorknobs before leaving the house at night time. That idea upsets my parents because what if a bad guy will come to our house and murder us all without knowing the doors are unlock. That is kind of scary. How irresponsible of him to do such thing. I think he is old enough to think/understand what is right or not, and leaving the doors open at night time is just upsetting.