Wireless headphone with low enough latency that the delay is not perceptable (applications include musical instrument amplifiers, television with headphones).

If a traffic light has a green arrow next to a light that is red, a driver with low attention could mistake the straight lane for having a green light.

Octave specific guitar amplifier

Sensitive microphone with heavy amplifier
before high resolution quantizer for low volume
hardware software Shazam style application.

Require train companies to post train schedules to integrate with Google and Apple GPS to reroute around train crossings.