Almost 13,000 households in Scotland will be able to see exactly how much they are spending on electricity as new "smart" technology is installed in their homes.

About 10,000 Scottish and Southern Energy (SSE) customers, mostly in Tayside, and a further 2640 people signed up to ScottishPower in South Lanarkshire are taking part in the trials.

Special display devices will show people exactly how much the electricity they use is costing them in real time - allowing them to see how much they could save by switching off various appliances.

Alternative readings will be available in carbon dioxide emissions, to demonstrate the impact of energy use on the environment.

New so-called "smart" energy meters will also replace old models, sending providers exact readings to end the current estimated billing system.

The firms are match-funding a £10m government programme for about 23,000 homes in Britain co-ordinated by energy regulator Ofgem.

It is hoped that the scheme, which received a boost in the 2006 Budget from Gordon Brown when he was Chancellor, will reduce the amount of electricity people use, helping both them and the planet.

A spokesman for SSE said: "By giving customers information on what they are spending at any given point in time they can see the impact of leaving on that light or keeping the TV on standby. Or the difference in cost between filling a kettle for one cup of tea and only half-filling it.

"We have already done some ad hoc trials with similar devices and the feedback we have received is that it really does change people's attitudes and behaviour."

Referring to the smart meters, he added: "They will send us accurate information on what customers are using for acccurate bills instead of estimated readings, and customers will also be able to see what they are using too."

SSE hopes to start putting in the devices this autumn. ScottishPower began installing the real-time display units in April in East Kilbride, Hamilton, Motherwell and Bothwell.