The Pedestrian Awareness Noise-emitting Device and Application is a speaker system that was described by school media as a low noise that "wasn't a car engine and was a bit closer to a muted jet engine, with some static and white noise thrown in." Graduate students Everett Meyer and Bryan Bai developed the system during their free time and created a company, Enhanced Vehicle Acoustics, under which they developed they prototype that is currently installed on Bai's Prius. PANDA is quieter than an ICE (by ~5 dB from the front and ~10-20 from the back) and emits a sound from the front wheel wells and under the rear bumper. What that sound will be in a future production version is not yet set, as the two will be working with various blind advocacy groups in the near future to find the most effective beeping, pinging or roar.
UPDATE: typo fixed
[Source: Stanford via EVWorld]