When is it OK to use deadly force in protecting yourself and your family from a home invasion?

There's a lot of discussion today in Minnesota around how to protect yourself during a home invasion. 

The four pillars governing the authority to use deadly force in MN are:
1. Must be in reasonable fear of great bodily harm or death.
2. Must be a reluctant participant.

3. Must have no reasonable means of retreat.
4. No lesser force would suffice. Deadly force was required

In a home invasion, you may not have to retreat, but all three of the other elements must be present in order for you to use deadly force. Other states have slightly different positions on this, so check out your state guidelines for the use of deadly force in your home.