nixos/system/home/swayidle/default.nix

{ ... }:
{
  imports = [ ../swaylock/default.nix ];
  services.swayidle = {
    enable = true;
    timeouts = [
      {
        timeout = 60 * 15; # 15 minutes
        command = "swaylockfx";
      }
    ];
  };
}