How do primary enforcement seat belt laws work?

Here’s a related question. I drive a very old car now with those terrible automatic seat belts plus a separate buckling lap belt. I always use the lap belt but would not using it be a violation?

It depends on what the law of your particular state says. Wisconsins law says

In this subsection, “properly restrained” means wearing a safety belt approved by the department under sub. (2) and fastened in a manner prescribed by the manufacturer of the safety belt which permits the safety belt to act as a body restraint.
So if the owners manual prescribes using both, you’d be in violation here if you didn’t.
Ten bucks shot to hell!

Yes, because proper use is both of them being fastened.

Worse, if you ever had an accident without your lap belt fastened, even a minor one, the automatic belt would restrain your upper body, but nothing restrains your waist & lower body – so you would break your spine, and be pluralized from the waist or neck down. Buckle up!

Would be fine, if it worked out that way.

But too many of them are not killed, just badly injured and we the public pay for their high medical costs & recovery. Or worse, they suffer traumatic brain injury and are confined in a state institution for the rest of their life, at taxpayer expense.

Does your business plan include the cost of liability settlements, when people are seriously injured due to wearing your invention, rather than their seat belts?

It could even be securely attached. You know, so you don’t lose it.

The instructions clearly state that you must wear your seatbelt in addition to the sash for safety purposes.

Pluralized? Is that where the belt cuts you in two?

The thing is, the cop can stop you for any reason that looks like a violation to him, even if he’s wrong. By the third time the same cop pulls you over (and you have a seat belt on), I would imagine you might be able to make a harrassment charge stick.

Do you think that would save you, when the injured victim and their innocent dependents appear in front of a jury?

Ha!
It’s what happens when you misspell paralyzed, and are lazy enough to let spell-checker fix it for you.

But cut in two is good too.

Items like TriPolar’s usually carry a ton of “amusement only” disclaimers.

Again I say: Do you think that would save you, when the injured victim and their innocent dependents appear in front of a jury?

There’s more than a few now-bankrupt companies that thought some ‘magic words’ would protect them, until they came up against the common sense of a “jury of their peers”.

IANAL. If I planned on marketing such an item, I’d get an attorney to assess my potential liability in the event of product misuse.