Hallowe'en laser maze. Build in a garage or something and use fog machines to let the green lasers really come through. Don't let the lasers get you in the eye. I use the kind that scatter pinpoint holiday laser light across the front yard, with the diffuser in front taken out leaving just a clean green beam.
This year's version has up to 8 trips and lasers, or fewer lasers if you are handy with mirrors.
Uses a TSOP38238 IR receiver for the MagiQuest wand "magic" function, not needed for basic operation.
Uses 2 x Arduino Uno R4 Wifi; 1 x TSOP38238; 8 x LDR modules; a few pushbuttons, 2 x Powerswitchtail 2 (one for switching a 12V supply for my flashing red beacon light and one to switch on and off the 'hard" mode lasers from the second Arduino).
I highly recommend Uno screwshields to make this project semi permanent. 7zip recommended as that's what the Processing app is zipped up with.
Aim lasers at LDR modules, when they are tripped, alarm sounds and Processing 4 show updated. Pics and vids likely to follow when I have time. Until then, here's a link to get the software (can one of the regulars here please check that I've only saved the link to the laser maze project? I don't do Google office type sharing stuff at all so want to be sure, if someone doesn't mind).
Credit to all the example sources I integrated into making this work and especially to @Robin2 as always whose Serial methods just work.