Some tournaments allow you to take breaks away from the board. If you're at a venue with a balcony (like the St Louis chess club), someone could give you light

Some tournaments allow you to take breaks away from the board. If you're at a venue with a balcony (like the St Louis chess club), someone could give you light signals from a parked car. That's a relatively low tech solution, it gets crazier from there as other people are saying here.