Along with food and water, reliable electricity supplies are rightly considered an essential of modern life, even with the environmental issues regarding power generation.

Mains electrical energy may well be a must-have but it’s certainly not free. And today’s switched-on consumers often face energy "bill shock". Electricity may be hazardous but this has always been assumed to one’s health rather than wealth!

The complete Cent-a-meter OWL system: wireless data unit at left, sensor almost hidden at rear and the sometimes confusing display unit at right.

In spite of improving appliance efficiency and better-insulated homes, soaring electricity bills often are due to ignorance about just "Watt" in their home is using the family "Joules".

Incidentally, the Joule is the unit of energy while Watt is the unit of power. Watts and Joules are related: Energy = Power x time, so 1 Joule = 1 Watt x 1 second. By contrast, 1-kilowatt-hour "unit" on your electricity bill is equivalent to 1kW for 1 hour = 1000W x 3600s = 3.6 megajoules (MJ).

Consumers’ attempts to ease electricity consumption, both sensible (energy-efficient lamps and appliances) and half-baked (wrapping in blankets/sitting around a candle/cold showers), may be futile if the true culprit is a power-hogging beer fridge in the garage or the pool pump being on for unduly long times.

Short of balancing on a chair while trying to read a dusty switchboard meter, it’s not easy to relate high power consumption (arising perhaps from an earlier cold spell) to accounts received weeks later. Behaviour modification usually best occurs when associated with feedback at the time – you don’t stop a dog chasing cars by scolding it weeks later!