Two approaches I have to this (and bear in mind that I'm agoraphobic, which is a lot like hypervigilence gone mad), premised by: noticing shit isn't the problem, it's getting distressed that's the problem.
Example: noticing whether people are hidden under cars. Is that a Jason Bourne thing where people might be hiding under a car waiting to...er, scramble to their feet and chase me down? Or is it at the other end of the spectrum, which is actually just Mindfulness, like, wow, guy under the car, noticed that, that's weird, what else around me right now am I noticing? My hypervigilence is somewhere on a spectrum: Jason Bourne style? Distressing, problem. Mindfulness, good thing. Tricky!
So, first, is it interfering with my function? Buses drive me batty, but I don't need to use buses. No problem, avoid buses, Ragdoll one, hypervigilence nil. Sitting in a classroom? Waaaay stresful, but I need to be able to do that. I make it as comfortable as I can and, yep, have to fight it. Gotta concentrate on my lecturer, not people walking behind my chair. Function impairment means time to intervene, otherwise? Pfft!
Second, is it causing distress? Walking down the street again, noticing people under cars. Is it causing me distress? What I'm actually monitoring there, though, is my SUDS, not "how much stuff am I noticing". If my suds go up? Yes, time to combat the hupervigilence. If not? It's just querky, not actually a problem. It's the distress, not the actual 'noticing' that I'm focused on.
Funnily enough, if I did ever notice someone under a car, I'd probably be more concerned about whether they're okay than whether I'm okay. Why afe you under a car, because that doesn't seem like a safe place to have a snooze!?! So, that's a pointless thing for me to be worrying myself about. Pointless worry? I try and focus on other stuff (ironically, I turn to mindfulness!) because there's better things my brain could be doing with its time than just plain pointless worry. But then, worry and hypervigilence are 2 different things, and worry is something that I throw my cbt at...which is a different thread entirely!