As long as Tesla's cars are so quiet you should, in addition to the usual horn, having one with lower/nicer sound to make pedestrians and cyclists aware that you're driving behind them when you need to let them know.
The GM EV1 had this feature. When driving below 18MPH (or so), you could flash the lights which would also emit a pleasant tone to warn pedestrians. I used this feature several times, but the pedestrians just looked at me quizzically.
Soon all electric cars will have to make noise as long as the car is on and moving >18mph. The government doesn't think you can do it on your own so they are jumping in to help.
Most cars on the road make noise currently and you still have car pedestrian mishaps. You can't fix stupid. Just like brake lights!! they are only effective if you see them!
YESSS!!! And not just electric cars, regular cars as well. Sometimes you don't want to scare someone and just let them know you're there or whatever other reason...I've been thinking this for the last couple years.
Hopefully Tesla will notice this and I'm sure with a simple software update could have a lower volume horn with flash of headlights under certain speeds.