The ThermoSmart uses about 2 watts of energy. That is very little. As a comparison, most TVs use 5 watts on stand-by. The electricity costs for the ThermoSmart are 4 euros per year (2 watts x 24 hours x 365 days x 0.23 euro/kWh = 4.03 euros).
The Wi-Fi connection in the thermostat is the biggest user. But this allows you to program your thermostat anytime and anywhere. Studies show that people who have not set their thermostat correctly use up to 20% more gas. That is 150 euros a year for an average family. Those 4 euros you pay to easily program and operate your ThermoSmart are paid back double and more in gas savings.