If you decide to set up an SDR for ADS-B, you might want to consider setting up a WebSDR with something like OpenWebRX. This would let people listen to all the signals in the bandwidth that you set.
If you're interested, receiverbook.de is a list of most WebSDRs.
If so, you might want to look into turning off bluetooth absolute volume. It's supposed to keep volume syncronised between your bluetooth device and your phone/laptop/etc, but some headphones don't seem to support it, wich can end up with them setting their internal volume to max.
Nope, at least afaik. Prototyping and building cars by hand (without a whole factory set up to build it) is hard. Not to mention extremely expensive. And you have to build multiple (identical) copies of the prototype to get it street legal, because of crash testing. And you have to be able to guarantee that what people build with your kit remains identical to your prototype. Or everyone assembling such a kit would have to build multiple copies of the car and go through the certification process individually.
And of course there are very few people that would want to assemble their own car, so you wouldn't be able to make a business out of it.
I'd like to elaborate a bit on why DNS can be used to track you.
Nearly all web traffic is encrypted (https), you can check by looking at the padlock next to the URL in your browser. But DNS requests aren't encrypted by default. This means anyone, most likely your ISP our the admin of your home network, can see what domains you're accessing. That means just google.com, lemmy.world, etc. and not lemmy.world/post/.... This isn't a huge amount of info, but it does tell anyone who's looking approximately what you're doing (googling something, looking at lemmy, etc.).
To fix that there are a few different ways to encrypt DNS requests, the most common of which (afaik) is DNS over HTTPS, which will encrypt DNS requests like any other web request your browser makes. I don't know why this hasn't been made the default yet. Firefox has a setting for DNS over HTTPS, it calls it secure DNS.
Amateur radio/ham radio. There are a few ham radio communities on lemmy, but they're all fairly inactive. I occasionally check on some groups on matrix as well.
The next few years are looking quite exciting for ham radio, because we're reaching the peak of the 11 year solar cycle. This gives us amazing conditions for long range communication.
A small, cheap holographic projector (as in projects a glowing volumetric image into the air that I can wave my hand through). It would probably work using femtosecond lasers, but making the optics small and cheap would be difficult.
Are you perhaps looking for an Expression?
I think that is probably as close as you can get to what you want to do.