my favourite demonstration i ever participated in in class was a networking teacher telling us about mac addresses and how networks use them to direct packets around, and i asked "what happens if two devices on a network share a mac address?"
"mac addresses are globally unique, there are no two devices that share one"
"sure, right, but. there's software for spoofing your mac address, i used it to get my switch onto the walmart network when i worked there"
"true... i don't know, but my phone's mac address is up on the whiteboard, let's find out!"
it wasn't exciting, it just knocked us both off the network
but it was fun to learn something that nobody in the room knew
while i set up the software he said "by the way this might be illegal" haha
i confirmed later that it's not but like, my understanding is that the FCC will get your ass for a lot of invalid broadcasts so i understand why you might think it could be
your wifi router can be configured to broadcast on one of a number of channels, from 1 to 13 (i think they're sliiiiightly different wavelengths but take that with a huge heap of salt. for this post the technicals don't matter). this helps prevent network congestion. signals on different channels won't bump into each other as much
i've attached an image of the networks near my house (come at me, rainbolt) and what channels my phone can detect them on. you can see that a network still interferes to some degree with the channels near it, so the only polite channels to use are 1, 7 and 13 for minimum pollution
you see that 14th channel i didn't mention? the one that's separated out a bit more? my understanding is that the fcc gets your ass if you broadcast there
i had a router once that would just... let you do it. it was in the dropdown menu. i never tried it because i was afraid of the fcc getting my ass
@monorail fyi the allowed channels are set by a country parameter that may or may not be user-settable depending on the device
also the fcc don't drive all over the place checking wifi channels ofc but if someone complains (amateur radio ppl) they will probably let you know. A ton of ppl's wifi is misconfigured so the chance you'll get punished is probably very slim
@monorail oh and you could probably cross-reference ssid searches on wigle and find your location exactly but I've already gotten rate limited from a few cursory searches so I won't bother