They know, it's just that the ad is written for all the welfare moms who are hoping for a bigger check.
I'm guessing it said she is not pregnant and the guy is like "OMG Sweet"!
Maybe it's ultra effective and is testing for the next pregnancy
@MisterSardonicus, from the looks of the guy she'd better hope it tells her who the father is.
PLOT TWIST: The little device simply says, "You just plssed all over your fingers!"