Does the Ring Alarm work without wifi or home internet?

I live with roommates and i need an alarm system to make sure no one enters my bedroom when i am not home. I thought of buying a Ring camera, however since those only work if the WIFI is on, it would be very easy for a roommate to disable the wifi/turn off the power and then enter my bedroom. So my questions are: 1. Does this work without wifi/home internet at all times? Does it have its own 3G/4G/5G network? Of course it will be connected to the wifi when i am home. But i will have to turn that off, once i leave my room. Is this possible? Can i turn off the Ring Alarm systems connection to the wifi so that it will rely on its own 3G/4G connection for a few hours while i am gone? 2. Does this work with a battery system, similar like the non plugged cameras? 3. Will it notify my phone whenever someone opened my door? Thank you in advance.