You can buy Nest's temperature sensor now
It's meant for houses with plenty of rooms -- or rooms with varying temperatures.

Nest's sensor can help regulate the temperature of larger homes.
The Nest temperature sensor announced back in March is now available for purchase.
Nest's temperature sensor is an accessory to the company's Learning Thermostat or Thermostat E, intended for homes with lots of rooms, or rooms with varying temperatures. Like the name suggests, the sensor reads a room's temperature and relays that info back to your Nest thermostat, so it can make adjustments accordingly. If you've got a Nest and ever wondered why 72 degrees doesn't feel like 72 degrees in certain rooms, your home might benefit.
The device is currently for sale on the Nest website -- though it looks like there's a 13-day wait at the time we're writing this -- and in stores like Target and Home Depot. One sensor costs $39 (roughly £29/AU$52 converted), but you can buy a three-pack for $99 (£73/AU$132 converted).