Carabiners are used also in mountain climbing. Basically you twist to unclip. So you twist and then open. Think of it sort of like a child proof medicine bottle where you have to press and twist at the same time. Except in this instance you have to twist in order to press. The people who are used to doing this motion, can do it quickly and efficiently. If you're not familiar with the system, it's a little tricky to do on your own and it's not going to happen by accident. You can't just casually grasp something and have it unhook on you. You're in a harness that's all clipped in and definitely not going anywhere. They put the harness around your legs and waist first and that part does take a few minutes. Then they clip you into the parachute thing after that. It's sort of a two part system.