Ghostbusters have a handheld device that detects “psycho-kinetic energy” (PKE), called, appropriately, the P.K.E. Meter.
Early in the library scene, Spengler is holding the device up in front of his eyes when he explains to Stentz that, “It’s moving.” So theoretically, there is some way by which it helps locate the source of PKE concentration. When we see the front of the device, it’s a bunch of small indictor lights, and impossible to make any sense of what we see there. (In fact, the later scene seems to have the orientation of the device horizontally flipped.) The inscrutability of the interface is fine, diegetically, since it’s a custom device built by scientists for themselves, but as they try and hire new ghostbusters and train them, they’re going to want to think about ease-of-training.
You might think that that green display we see in this first scene is pointing in a cardinal direction, i.e. just behind Spengler, but when we see the same device later, right next to the Keymaster, those indicator lights are spinning around a center that’s off the edge of the screen, so, again, the meaning of these lights is inscrutable.
Its most salient feature are the two arms that rotate out from either side, which are topped with a line of amber lights. When in the presence of high levels of PKE, the arms raise up and the lights blink more rapidly. At max PKE, the arms extend horizontally and the lights blink quite rapidly (see above). Unlike the user interface, these little guys are awesome. Let me explain why.
Both their lights and their extension help convey immediately the main point of the device: more PKE nearby. Notably they do so using two hard-to-miss signals that build on universal mental maps: up equals more, and faster blink is more urgent. Even if you can’t parse the UI, you get this. The immediacy means a lower cognitive load for the ghostbuster who’s attention needs to be on the environment around them primarily and on this device secondarily. Having physical motion and blinking even means it could be well in their peripheral vision and still convey the information. But it gets better. Even if it was out of sight, the motors that move the arms would provide a bit of sound and even haptic information that something has changed.
And lastly, we should keep in mind that ghostbusting is a service, and the customers are a vital part of that equation. Even if they don’t use it directly, they see it being used, and what it conveys to them as a touchpoint is important. If they are doubting, for example, the existence of ghosts, the little arms and lights would provide an immediately-understandable sense of whoa, and there’s a direct-feedback loop to verify that it’s not random. It’s detecting something in the environment. That would give the customers and onlookers a confidence that is important to new businesses operating within dubious domains.
So, seriously, those PKE arms are awesome and now I wish I had gone as a P.K.E. Meter for Halloween this year. Well, there’s always next year maybe at a sci-fi interfaces all-costume Halloween ball.