The battery-powered, inch-wide sensors are designed to be placed in different rooms around the house where they silently monitor how warm or cold it is.
The white puck-shaped sensors continually relay this information to the companion thermostat, which responds by adjusting the central heating system to keep those rooms at the temperature level the user specified.
Nest started taking pre-orders for the Temperature Sensor in March, but is now selling them direct from the website. Each sensor costs $39, or $99 for a three-pack, and comes with wall mounting screws and up to 2 years of battery life. Up to six sensors are supported per connected thermostat, and up to 18 are supported per home.
Customers looking to pick up a Nest Learning Thermostat or Nest Thermostat E can also order the Temperature Sensor as part of a bundle pack, which gets them $20 or $10 off the standard price for a single sensor, respectively.
Nest products don't integrate with Apple's HomeKit setup, but are popular competing connected home solutions. See the Nest website for more details.