This article needs some additional information:
1) Copulins aren't produced (or are produced in very low numbers at the most) if you're on birth control.
2) Copulins are produced in small amounts throughout a normal ovulation cycle, but the body cranks their production to max during ovulation. So, you'd probably have to be ovulating for this to work.
3) Women who have sex regularly tend to produce higher levels of copulins than women who do not.