How does one not already know that they had a hard braking event? Surely the jamming their foot on the brake pedal and the rapid deceleration would send an even more obvious signal than playing a chime?

Have you used one of these apps before? They capture a lot more than emergency stops, what I would classify as the above normal brake effort but not hard braking. Im sure the data exist to set the cutoff but its a lot more than “jam your foot on the pedal braking”.

It’s still out of the norm braking for my style of driver but from what I see on the road, people drive aggressively like this. Especially in the US.

What are these apps or devices? Where can I get one?

They are provided by your auto insurance company. A potential privacy nightmare, they track your movement. They also can get you a much lower rate.

If you don't want to go through your insurance company you can check out an app we built called RoadClub. You get points for safe driving behavior - and you can get the hard brake alerts. Is it a bit annoying? yes. You can't just drive agressively - you need to give space to slow down. I still struggle with it.

Your faq doesn't mention anything about location data. I'd like to try it, but want to know about that first.

Obviously people know, but theres no impulse to introspect on why or how. Knowing that someone else knows you had a hard braking event taps in to our social brains to provide a much stronger response to the event. When we know people are watching we're more likely to try and justify our behaviour.

A lot of people don’t realize that what they consider normal driving is actually aggressive driving by other metrics

I know way too many drivers who have exactly two modes: Full brakes and full accelerator. Like, they'll see someone in front of them, slam the gas pedal, and then when they get too close, slam the brakes to slow down. No in between. And they don't even know they're terrible drivers since they've always driven this way.