Below is a picture of the 3D printed prototype button to trigger the horn. It is attached to the handlebars with an adjustable Velcro strap. It stays right around where your thumb can easily push it without interfering with controlling the bicycle through steering and braking. It is designed to be water-resistant against normal rainy riding.
The design of the button is extremely important for the function of the horn. Users must be able to feel where they are meant to push by touch alone. As beta-tester Gregory put it “my finger hovers over the button instinctively when I see obstructions ahead.” Below is a closeup of the protruding soft-rubber piece with the Loud Bicycle logo indented in the center. You will be able to center your finger on the button and honk while keeping your eyes focused on the road.
The 3D printed rubber was a little brittle so we found another material to do tests with. I didn't have a banana so here is a quarter for scale.
To see what the button looks like now, checkout this follow up post with the Loud Bicycle button.