The ecobee SmartSensor Room Temperature Sensors are a pack of 2 white sensors that are powered by 3V button cell batteries. They are wireless and have a display size of 3.5 inches, making them ideal for monitoring room temperatures in your home. These sensors are compatible with various smart home platforms like eWeLink, Apple HomeKit, and Google Home, allowing you to easily control your heating and cooling systems. With a sleek rectangular design and easy wall-mounting capability, these ecobee SmartSensors are a convenient and efficient addition to any thermostat setup.