I think one fun application would be a light which represents your wi-fi strength around the house. Obviously in a smaller apartment that's really not a problem, but in larger houses it would be fun to see.
Another application would be to find hidden RF sources / leaks. I have a home recording studio, and for the life I could not find some RF source that kept adding noise / interference. I could roughly detect the frequency of the noise, but not its origin. I guess if I had a couple of RF sensors I could try to triangulate my way to it.
But tuning in to the specific wifi channel you router use you could even use this piece as a signal strenght plotter!
I guess it's a good commentary on how tech people value other peoples work.
I was just thinking about this the other day, and wondering about directionality...
For example, if you had a camera facing a space, and the receiving antenna was within that space... and you were able to (somehow?) from the antennas perspective, see the "direction" the frequency was coming from..
And then map the different specific frequencies within the desired bandwidth to colors... and of course intensity map like you have in the slit device..
And then "look through the camera"... you would see a live three dimensional overlay of all signals within range (colored!) "interacting" with the antenna... but kind of more the "looking through the camera" sort of view, like you could "see" how those waves were interacting..
And then wouldn't it be interesting to put a tin-foil hat to one side of the attennas.. and see how the waves change in real time... etc.!!!
(I guess it takes three antennas, to triangulate the field? Maybe all three can still be mounted on a single device in close proximity?)
And every time I see something like this I like to remind to myself and imagine what spherical grid of Starlink satellites linked by laser is really capable of instead of mere internet as it is advertised.
You can kind of do that quite easily at low frequencies, by measuring the phase of signals coming in from a pair of aerials. If you put two aerials a quarter of a wavelength apart and switch between them very quickly at audio rate, then you'll get a tone when there's a difference in phase. If there's no tone the two signals are exactly in phase - the two aerials are exactly the same distance from the transmitter.
If you look on some police cars you'll see a group of four aerials about 15cm apart stuck to the roof which used to be used for "Lojack" style trackers.
There are a whole bunch of circuit diagrams floating around for doing this kind of thing, with the simplest being Ye Olde 555 timer and a couple of PIN diodes!
(and they cost like 5ct each)
What would really finish it for me, though, is if, when the button is released, the device shows a website, with URL visible, with a photo of the criminal, with added facial recognition and lookup of social media to find their identity.
What fun!
We're bathed in EMF. It's what light is, but aside from that we use electricity so much now, we're in a sea of radiation in other frequencies too.