I used to put a fake gift or two under the tree years ago for the lols. Nicely wrapped boxes with a rock or piece of wood (and packing material) but always had great real gifts for the recipient after their trauma.

The last gag gift, if you can call it that, was a stack of $300 in $1 bills with a $100 bill on the top and bottom that I gave my gf's son the Christmas after he totalled his first car a month earlier. Man did he light up thinking it was a $5K stack! Lol! Then watching him come to the realization he was off by $4500. Regardless, he was still happy as hell to get it. I told him it was the money he could have saved on insurance if he hadn't crashed his car. Then we told him to look outside in the driveway ... there was a decent winter beater I picked up cheap parked out there with a big bow and ribbon on it for him. He had a good Christmas.

That looks like a cool project! I hear relays and solenoids when up close though.