
http://www.digital-watch.com/DWL/1work/seiko-0439-5009/
i think it has a spring on the upper and under side of the caseback that you have to push in with a small screwdriver to open the case.
But i'm not 100% sure...so if you see no little gap to put your screwdriver in to push the spring, it maybe is done different.
here you can see the spring if you look carefully
