This setup-and-forget countdown timer that activates 10 relays for the last 10 seconds of the year. Like a switch, a relays can turn on/off anything that can be turned on/off. So, this project could just turn off all the lights in a house for a dark and private NYE, to blaring ten electric boat horns for the annoying party.
Do anything you want with the relays… I chose to launch a single firework at the zero second. I chose this mainly to give a simple way of handling launching of fireworks remotely. (I would like to add, much safer too. No more light the wick and run like crazy…)