This is one of those things that wouldn't exist in a fully realized solarpunk world, but might be useful during a transition.

This camera assesses drivers behind a cyclist to let them know when someone is coming up behind them, and other driver behaviors. One idea I particularly like:

A major bonus is that data gathered from Copilot devices can prove useful to aid local authorities and road safety organisations seeking to make cities and towns safer for cycling. “We are in the middle of starting a partnership with the city of Pittsburgh,” says Haynes, “where we’re going to deploy dozens of these Copilots with people that bike to work and use that to actually inform where do we need to improve the bike infrastructure?”