Bring the class together and ask pairs of pupils to explain the reasoning behind their answers. For example, if it is too cold, then turn on the fire. If it is too hot, then turn on the fan. If the temperature is about right, then do nothing.

Explain that systems in a home can be more complex than those that pupils considered in their last lesson because:

· more conditions are being monitored, such as the time of day, air temperature, water temperature, air quality, light intensity, whether windows or doors are open or closed;

· more outputs are being controlled, such as room heaters, immersion heaters, refrigerators, automatic lights, automatic blinds, the garage door, burglar and fire alarms.

Remind pupils that in these systems constant checking is going on and that each check involves a loop.