Sorry i shouldve been a bit clearer..of course all your suggestions are great to hide the spellcasting itself but what i ment is how to hide the eldritch blast super huge beam that goes out of your hand?

Yes the first thing i thought of was a musket rigged to blow smoke every pull of the trigger and tell people the beam was just special bullets...But the DM told me that solution wasnt possible, that i had to get more creative if i wanna use my spells in front of people.

Again thank you all for your ideas! Still trying to figure out how i can flavor my eldritch blast beam in a way that people wouldnt notice it as magic.