Gili Air is full of demon refugees from Bali and its near islands. You see, tomorrow the demons will inspect Bali to look for people. So if everyone stays home and there is nobody to be seen, the demons will be disappointed and leave the island for another year. Balinese demons are not very bright.
The trouble is that the Balinese take this very seriously. On the Day of Silence, everyone must stay indoors, including visitors, all the windows are darkened, all shops, restaurants, and transport close, and electricity, the phone system, and the Internet are shut down. Even hospitals lose power, although I suspect they’ll have a generator hidden away somewhere. No electricity means no air conditioning or fans in this heat, and frozen food (ice cream!) will spoil.
But, no demons. Priorities.
The Gilis are part of Lombok, not Bali, so all the spoilsports congregate here. I walked once around the island to see the low-key bars and hangout spots on the north-western side. Very relaxed, good food, and the island is so small that the loop takes less than two hours of walking.