What is your objective?

If it is to stop the robbery and get the guy to flee, dial 911, turn on an outside light, and yell to him the cops are coming.

If you want him caught and prosecuted, call 911 then get the camera/video cam and start recording.

In no event would I go outside to arrest him before the cops get there. I would, however, have one or more firearms handy in case he tries to take stuff out of the house, too.

Remember the guy in Texas who went out after being on 911 for a while because he wasn't going to allow them to steal his neighbor's stuff? Killed both robbers, and was eventually acquitted but your results may vary. He very well could have ended up in prison for life.