[quote=@DizzyRenegade]
Well magic doesn't necessarily break technology. One thing that stuck with me was when Harry was saying that in the middle ages magic made milk curdle or infertility and that changed with the turn of the 20th century. So I was thinking that magic would disrupt something that's not technology during the turn of the century to create a parallel world where wizards could use technology
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Interesting idea.  Well, what I was thinking of as a first world(after we get lost in the neverwhere) would be an alternate future where the red court won the war.  I like your idea of a different tell for wizards.  So what about radiation of some sort?  Perhaps the redcourt, in an effort to make sure that wizards don't come back into power have launched a smear campaign to make it seem as though the wizards are the ones responsible for the sudden amount of deaths that have been occurring since the war's end?  There could be patrols with devices to scan for the type of radiation that wizards give out?

Another possible tell is that people are becoming more sensitive to magic and so when their around a person with magical abilities it creates this strong feeling of terror?

Also, another alternate world I was thinking about involves that drug ThreeEye.  The one that allows regular people to use the wizard's sight.  Well the creator made a different batch, one that made permanent changes in people's brains.   So instead of just temporarily seeing things only a wizard normally could see it'll become so that all they can see would be what the wizard's sight would show them.  So of course a lot of people would become insane.  Not only that, but in certain cases people would gain magical abilities of varying levels.  Needless to say the world would be pretty chaotic.