A valid concern, but that's where other senses come in for me, primarily hearing (no disrespect for any deaf gamers out there of course). Not many enemies attack without some kind of sound, or battle music. If the world is still spinning while you're reading your pip-boy I'd expect the sound to still be in the background even when in a pip-boy game. Also I've never really been in a situation in FO3/NV where I couldn't be assured an area was cleared and I wouldn't be attacked while standing still, they always come out of nowhere if I'm moving and not paying attention.