I was given one of those free by EDF some years ago as an energy saving device and I use it on my PC so that when the base unit is switched off it also switches off my monitor and printer. I works fine. Try checking with your electricity supplier, there may be some free ones out there. I also have a free electricity usage monitor from EDF.
Sony Xperia Z5 review: Hands-on with the phone which the Z3+ should have been