Amazon currently lists the pack of two SONOFF TRVZB thermostat heads at 51.34 €, a 15% discount from the recommended price of 60.40 €. The device is designed for users who already have a Zigbee gateway or a system like Home Assistant, a popular open-source home automation platform. The SONOFF TRVZB replaces the original head on a hot water radiator, using an M30 x 1.5 mm thread, and comes with adapters for compatibility with most heating systems. It communicates via Zigbee 3.0, a wireless communication protocol commonly used in smart home devices, and allows independent control of each radiator. Each SONOFF TRVZB head can be programmed to follow its own temperature settings, between 4 and 35 °C, and manage time slots over 24 hours. It includes open window detection, which identifies when a window is open by detecting a temperature drop of more than 1.5 °C in 4.5 minutes and automatically cuts the heating. The device can be controlled locally using Home Assistant through ZHA or Zigbee2MQTT, without requiring cloud-based services. It operates on three AA batteries, offering an autonomy of more than six months, and includes anti-freeze protection that activates automatically if the temperature drops below 5 °C. The SONOFF TRVZB is specifically designed for homes with a boiler and water radiators in rooms that are not all occupied at the same time. It has a screen that displays the temperature, mode, and battery level, and a knob that can be locked with a three-second press to prevent tampering by children. It can also use an external temperature sensor, such as the SNZB-02, to measure temperature in a different location than the base of the radiator. However, it is not suitable for electric radiators and requires a Zigbee gateway to function. The SONOFF TRVZB is not intended to compete with all-in-one smart thermostat solutions like the tado° Smart Radiator Thermostat X, which is praised for its user-friendly app and quick installation. The SONOFF TRVZB assumes users have experience with Zigbee devices and existing home automation setups. For those starting from scratch, a complete kit may be easier to install. The current price of 51.34 € for a pack of two is higher than the 23.76 € recorded in February but remains a reasonable option for those with the necessary equipment. Before purchasing, users should check the type of valve on their radiators, as this is a critical factor in compatibility. To take advantage of the Prime Day offer, users must first subscribe to an Amazon Prime membership, which starts at 6.99 € per month.