Happy with this code, thought I'd share

(dolist (h `(kill-emacs-hook focus-out-hook))
  (add-hook h (lambda (&rest _)
                (shell-command-to-string "~/bin/fntoggle off"))))

(add-hook 'focus-in-hook (lambda (&rest _)
                           (shell-command-to-string "~/bin/fntoggle on")))