On the issue of the car being too quiet around pedestrians, someone suggests putting hockey cards in the spokes 
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You're closest to what I'd actually like to do: I want to use a bicycle bell. Maybe hooked to a solenoid to sound it.
I'm actually already fairly concientious towards pedestrians since 40-50% of the time the Blackfly is moving, its engine is off. I often tap the horn to let people know I'm there.