Audible warning if handbrake is engages and vehicle is moving.

[kinyo]

it is easier to develop the habit of checking your handbrake than tinkering with your car's electricals

[straker]

I know, which holds me back. And I don't trust that to any car electrician either.

But if there are accessories that can do this with the least mangling of car wires, I'm interested.

[dr. d]

you might try tapping into the wire that sends electricity to the idiot warning light in the dash.... from the engine bay. look for it as it exits the fusebox.. at least there, you have more elbow room..
you can use it to activate a small buzzer... or the enterprise's red alert wail!

i am assuming your car has its fusebox in the engine bay, like other cars..
even the 'box above the driver's left knee is difficult to work on..

or you can try and access the mechanical switch that the brake lever de/activates when it is pulled up..
this should be easier and less dangerous to splice into..

good luck.