Cooking with your eyes, ears and nose is the safe way to go!
I always want to make sure my food looks cooked, smells great, and sounds like the simmer it should.
That said, it's important to use those same senses for safety. Keep an eye on food even if it's staying in the oven for a long time; make sure to keep an ear out for any unsure sounds that might mean you need to attend to your food; lastly be sure to smell your area for any smoke or burning so it doesn't do any damage.
It's a good idea to keep the fan on at least low when you are leaving something to cook for a while as an extra precaution, especially if your smoke detector seems to be EXTRA sensitive like mine!