I would not advise using a knife on an intruder as stabbing someone does not stop them and 9/10 the weapon will be used on you. Pepper spray is much better as it will disarm the intruder allowing you to flee.
Too many women think a knife or some sort of club will have an effect, it wont. Get pepper spray. Or as you are in the USA get gun-trained and get a small effective gun like the Ruger LC9s (9mm)
But I stress get trained on how to use it and get plenty shots fired at your local range. The Ruger is made in the USA so helps make America great.