Households could cut their fuel bills by £80 a year with the help of a simple "smiley", a study has revealed.
Giving people feedback on how much energy they are using compared to their neighbours can have as big an impact on reducing bills as installing loft insulation or upgrading their boiler, the research by the organisation Sustainable Homes found.
Sending people happy face emoticons, or smileys, if they used less energy than other similar households, and sad faces if they were using more than the rest of the group, led to people changing their habits to reduce electricity and gas use.
The success of the smileys could be down to people's desire to "fit in" with the social norm, something that can be a more powerful driver to change behaviour than the motivation of saving money, the study's authors suggested.
Andrew Eagles, managing director of Sustainable Homes, said: "These findings will be of great interest to anyone concerned with cutting energy bills - which, of course, is most of us.
"We know that people are always keen to save money, but what this study uncovers is that their natural desire for approval is at least as important, and probably more so.
"Nearly one third of the UK's emissions come from homes, and the results have implications for the roll-out of smart meters in the UK.
"They suggest we would be missing a trick if we did not take people's real motivations into account with a simple and cheap method like this when we try and reduce household energy consumption."
The study recruited 540 homes in 14 housing associations around England, with all the households being given energy saving tips before they began the programme.
Some households received information about their energy use without comparison to other homes, some were ranked against similar properties and a third group received feedback with smileys which indicated how well they were doing compared to others.
Those in the smiley group whose energy use was in the lowest 25% of households got a yellow smiley with a big grin, while those in the second lowest quarter got a green smiling face.
Households whose energy use was in the second highest quarter compared to the group as a whole received an amber neutral face, and the highest energy users were sent a red sad face emoticon.
Feedback of any kind helped people cut energy use, but the research found that people who received smileys made the biggest savings compared to groups who were given a ranking or simply informed of their "killowatt-hour" usage.
The smiley group saved an average of 8% on their electricity bills and 3.6% on their gas bills, or around £79 on average.
If three-quarters of the UK population were to achieve these kind of savings, it could save 2.7 million carbon emissions a year, equivalent to switching off Didcot power station for half the year, the report said.