Keeping a cat inside

My cat is NEVER allowed outside unsupervised without a leash on because 1) I live in an area with lots of predators (black bear, a mountain lion who lives in the hill right behind my house, hawks, and packs of coyotes), and 2) she has zero survival instinct. She was born and raised a housecat with several large dogs, and is completely unphased by anything and everything. The dogs will practically run her over and she doesn’t move to preserve herself. She is tiny too. I live with my family and they try to keep her inside, but there’s been a few times where someone doesn’t close a door all the way and she slips out. They’re a lot more nonchalant about it and aren’t hyper aware of it like I am. For example, when letting the dogs outside, I check to make sure she’s not around and I stand in the doorway so I could intercept if she walked over. But my family opens the door wide and doesn’t bother making sure she’s not hovering around waiting to slip out. She has a bell on her collar so I guess they assume if they can’t hear the bell she’s not there. Is there anything I can do to make sure she doesn’t slip out when I’m not around? An alarm on her collar? Any sort of training? A mat or something? If anything happened to this cat I would probably leave this world too to put it bluntly - she’s gotten me through a lot.