How would the app know if somebody became pregnant seconds after they finish? Sperm takes 15-45 minutes to get to the egg at the fastest, but the usual is a few hours JUST to reach the egg. Then the woman has to be actively ovulating, and the fertilized egg has to travel into the uterus and implant into the walls. That can take 6 to 12 DAYS! What is this app, magic?
Yeah, that part seemed odd to me too. I feel like it needs a couple of changes to make sense:
(1) It actually includes some means of monitoring arousal and orgasm (like an implant or at least a wearable; it wouldn't have to be on the genitals; even access to the spinal cord would give you sufficient data to recognize an orgasm (then again if it's like a cockring or testicle implant, it could plausibly read his sperm count as well)).
(2) It doesn't know if you're pregnant until a couple of weeks have passed, because you are absolutely right, implantation can take that long.