How about one that allows (while listening) to see auras? Over a century ago, Walter J Kilner experimented with chemical screens to expand the eyeās capacity to perceive information outwith the normal visible spectrum. One such chemical, Dicyanin Dye is still a strictly-controlled substance. Looking at a bright light thru the screens would instigate changes in the eyeās function, therefore the effect remained for the naked eye when the screens were removed.
More recently, an Australian inventor called Tom Beauchamp developed PranaView goggles which seem to use a similar technique, albeit using substitutions in place of the strictly-controlled chemicals originally available to Kilner. From this video review :
Thereās two models, this one here which is the āBasicā which which was actually used after you sensitize with āModel 2ā so youād use āModel 2ā for about 60 seconds while looking at a bright light, a lamp, anything but the Sun - then what you do is youād close your eyes and you put the āBasicā on which is pretty much a lesser contrast shift between infrared and ultra-violet so this is sort of like more of a mild blue
What I found after using these for the first six months was randomly, people at work and people walking around, I would see the colors around their head in absolutely full pastel-bright colors which would amazingly take me by surprise, to the point it was so incredible that it would only last for a few seconds because when it appeared you would actually shock you out of it
So perhaps the field could be temporary, with the effect slowly fading after listening, but with long-term use it could become more permanent, or something that you could learn to switch on/off as desired