"Hold on, let me scan your crotch with my smartphone" is about as likely to happen as "Hold on, please sign this form giving consent" for two people about to fuck. Let's be realistic here.
This also ignores the obvious issue of data leakage. You work/live in a location with objections to the use of birth control. What's stopping your boss from covertly finding out who among his employees is "sinning" or what have you.
I imagine that would be easily spoofable (though that obviously takes a bit more preparation than lying about having an IUD), and almost certainly raises some privacy concerns.
Not to mention the social aspects. "Awww yeah baby, let's do this thing. Let me just... take out my RF scanner and verify that you have an IUD."
