Deadly force can be used in some circumstances for self-defense. You have to reasonably believe that: You are in imminent danger of being killed or sustaining great bodily injury, The assailant is committing a burglary and is about to use physical force against the occupant, or The assailant is committing a kidnapping, robbery, sexual assault, or a felony assault. Your ability to use deadly force is at its peak if you are in your home. This is Colorado's Make My Day law. It is at its weakest if you are only defending your property, not your person.