Onno's watch on the bell tower is, in his telling, mostly sitting. The sensor on the outer wall does the work. It reports the temperature and the wind speed to him through a small chime that hangs by his elbow. He's written down two rules so that even on the nights he dozes, the right things happen.
The first rule, for the brazier: ? the temperature drops below freezing, light it. Reactive — it just waits.
The second rule, for the shutters: ? the wind is calm, leave them open. The moment the wind picks up past thirty, close them.