Beer doesn’t usually smell of ethanol, it smells like hops and yeast. Since most AF beers are built to model light ales anyway, I can hardly tell. I’ve also gotten really into mocktails lately and with the right mixes of bitters and syrups most of them are significantly better than real cocktails. With those, that gasoline taste of ethanol is noticeably absent in a good way!
I know exactly how caffeine affects me though, and would pretty quickly realize I’d been given decaf.