While everyone knows that Google uses user data to serve well-targeted ads, the search engine giant is said to be secretly testing a device called EnergySense that will monitor energy consumption.

The smart thermostat will be linked to the Internet, so homeowners can track their usage and make necessary adjustments.

The project might sound familiar to those who follow Google developments. The company toyed with the idea of helping businesses and homeowners understand how they consume electricity using PowerMeter, a project that was dropped in 2011. PowerMeter then featured an online dashboard that shows how people are consuming electricity but it never came into fruition after the company determined that there was lack of interest for it.

"Google has been registering non-employees to be 'Trusted Testers' of the service in St. Louis and possibly elsewhere," reported the online subscription publication The Information (subscription required), citing two sources knowledgeable about the project and documents it reviewed.

Consumers, however, should not expect a Nexus-like hardware for the smart thermostat since Google is said to partner with other device manufacturers, particularly Ecobee for the EnergySense project.

At the moment, the darling of the technology world when it comes to smart thermostat is Nest Labs. The company founded by former Apple executive Tony Fadell, was able to raised funds in support of its thermostat that can learn the homeowner's preferences when it comes to heating or cooling the house that will eventually lead to energy savings in the long run. The Nest Learning Thermostat connects to the Internet via Wi-Fi and can be manipulated using a smartphone.  Nest is now focusing on producing a smart smoke detector that can even call the fire department in case of emergency.

Other brands that have toyed with high-tech thermostats include Honeywell and Ecobee.

Google's EnergySense will make most of the wireless-enabled home appliances to monitor energy consumption. What can be tracked might include lighting, smart TVs, audio players, and other web-connected hardware.

Google has not commented about the smart thermostat development as of reporting. The details are very limited and it is not for certain if ever it will hit the production line.