Ants decide what category of work to do based on the numbers of different types they encounter. If they run across lots of foragers, they may be chemically signalled to become one too.
Today’s invention is an app which performs a similar function for urban-dwelling humans.
Wearing one’s phone with face-detecting camera facing outwards would allow a passive count to be made of eg smiles encountered during the day, or the relative numbers of different clothing colours (adjacent to faces).
It might even be possible to estimate the speed of movement of faces during a given day to arrive at some idea of the level of urgency among the inhabitants of different areas visited.
These data would allow one to understand what colours were in fashion and the mood of the local population, so that your own behaviour could be chosen to conform or differ -and without having to actively record any of these subtle observations.