By Marc Cieslak and Tom GerkenBBC TechnologyImage source, Getty ImagesUK households could save an average of £147 per year by switching off so-called vampire devices.Vampire devices are electronics that drain a surprising amount of power even when they are on standby.British Gas research indicates households in the UK are spending £2.2bn annually just for the privilege of leaving vampire devices on standby. This equates to £147 a year for the average household – the equivalent of two months’ electricity charges.