ventless propane heater

I want to install a propane gas heater in the bedroom for emergencies. In case the power goes off, we could stay in that room and not have to leave our home. Are ventless heaters safe? We live out of the city limits and the power does go off at times. ( we are on natural gas now). I just want to have a room that is heated if the power is off. Thanks for any information you can give.

Lucky