Size name:1 Pack The white Temperature Sensor from Nest allows you to maintain a comfortable temperature in any room of your house. This diminutive device works by sensing and communicating the temperature in a room to compatible Nest thermostats, which enables you to adjust the room temperature to what you want it to be. This sensor is equipped with Bluetooth Low Energy wireless technology, and has a working range of up to 50' away from your Nest Thermostat. An included CR2 3V lithium battery delivers up to 2 years of battery life. The free Nest app for iOS and Android devices enables simple setup and customization. Note: This temperature sensor requires an installed 3rd generation Nest Learning Thermostat or Nest Thermostat E, which are available separately. Requires an installed 3rd generation Nest Learning Thermostat or Nest Thermostat E Senses and communicates temperature to compatible Nest thermostats Offers flexible placement on a wall or shelf You can place temperature sensors in different rooms, and choose which room to prioritize Up to 6 Nest Temperature Sensors supported per connected thermostat, and up to 18 Nest Temperature Sensors supported per home Weighs only 1.6 oz