If you have a Withings Aura Sleep Sensor and a Nest Thermostat, you can link the two so that your Nest Thermostat automatically adjusts the temperature based on whether you’re in bed or not. If your Sleep Sensor detects your presence in bed, your Nest Thermostat automatically changes the temperature to 18°C - 20°C (64°F - 68°F) as it is the optimal temperature range when you’re sleeping. The previous thermostat settings are then restored once you get out of bed at the end of your night.
Both heating and cooling systems are used to adjust the temperature. It is not possible for the Sleep Sensor or the Nest Thermostat to use only one or the other.