How does a stand-alone airbag vest know when to go off?

The electronic ones like this run off an algorithm that watches acceleration data constantly. It's looking for a specific pattern of violent deceleration and body rotation that matches a crash, not just any bump. I've ridden a couple of seasons on similar electronic vests and potholes, speed bumps, even a low-speed drop in a car park never set mine off. The tradeoff is they need power and a bit of brainwork to decide, whereas tether systems fire the instant you leave the bike but only if you're actually separated from it. Both approaches miss things, just different things. Under layers it works fine. Electronic vests don't need a physical connection to the bike so they don't care what's over the top, as long as the outer layer isn't compressing them to death. My textile jacket had to go up a size to sit properly over the vest, and I pulled the foam back pad out of the jacket because the vest replaces it anyway. If your back protector slot is snug now, that's your real problem. The vest needs room to inflate outward, and a tight leather jacket will fight it. Try the vest on under your summer jacket before committing, some leathers just won't play nice. Battery wise, mine flashes and beeps well before it dies, and there's an app level warning too. I made a habit of charging it overnight like I do my phone and it's never gone flat on a ride. For a 10 or 12 hour day you should be fine on a full charge, but if you're running it off a power bank while riding, test that setup at home first, some power banks cut output when the draw drops low.

On neck support, honestly for street riding it's a nice to have rather than essential. It matters most in highside type crashes at speed. If it got more people wearing airbags who otherwise wouldn't, that's a net win.

I'm new to all this stuff, so I'm still learning how these systems actually work. Your point about how it works under layers makes sense, but I'm curious about somthing else. I mostly do city riding and lots of traffic stop and go. Does the vest feel really bulky or awkward when you are just sitting in traffic for a while? I worry about the sheer physical size when I'm maneuvering through tight spaces, not just during a crash. It feels like comfort in the city might be a totally diferent issue than long distance touring, even if the protection is there.

The one thing I'd want to know before dropping that kind of money is what happens after it actualy goes off. These electronic vests still use a gas cartridge, and those aren't cheap to replace, plus some brands want you to send the whole thing back for inspection before it's road legal again. If you're the type who drops the bike once a season in a car park, that could sting. Anyone know if Dainese lets you swap the cartridge yourself or if it's a send-it-in job?

I worry about the constant electrical brain running things. Back in the day, your protective gear was simple; heavy, maybe, but if you took a tumble, the impact itself did the work. You knew exactly when the protection kicked in becuase it was mechanical. All this smart tech sounds slick, but what happens when that sensor starts acting up or the system glitches mid-ride? It feels like another point of failure you've introduced into an allready complicated machine.

I reckon these high-tech gadgets still require more fuss than my old gear ever did. You gotta think about updates and software versus just trusting solid, heavy-duty material. Does anyone have any experiance with the required annual system checks or maintenace beyond just keeping the battery topped off?

I work the gear counter at a shop and the fit question is the one everyone gets wrong. I'd guess around 80 percent of customers try the vest over a t-shirt, buy thier normal jacket size, then come back complaining it feels like a straitjacket over the airbag. You need to bring your actual riding jacket when you test fit, zip it up, and reach for the bars position. If you can't raise your arms without the vest pulling at the shoulders, go up a size or pick a slimmer outer layer. Also check the chest strap sits below the collarbone, if it rides high it won't position right when you actually need it.