Energy-saving device cold call

[Flup]

Just had a cold call from the subcontinent congratulating me on behalf of the British government for paying my electricity bill on time. So nice of them to think of me. The guy went on to offer me a device which could cut my bill by 40%. Gosh, it's my lucky day. He was briefly speechless when I said 'sorry, I don't believe you'... then hung up a few seconds later.

I suspect this was either a useless-power-factor-correction-device scam[1], or just a ruse to get my credit card details. Thought I'd share it here in case anyone's naive relatives need to be warned.

[1] see e.g. http://michaelbluejay.com/electricity/powerfactor.html for thorough debunking.