a notice for your change AND a notice for a change from an unknown location that is not the answer, but if you are getting ONLY a notice for a change from an unknown location after your making a change it is probably your change with Facebook unable to know your location. Maybe? If you can get in using your revised password it is a sign that the change was actually yours. If you cannot get in without having to go through another change it is probably a hack.
In either case, changing your security question answers to a random mix of characters is still probably a pretty good idea anyway.