We all invent things in our heads: "I which I had a gadget that would?." Then every once in a while we discover that someone has invented it.
I live in Montreal. Winter is cold in Montreal and we are familiar with outdoor electrical outlets all over to keep our cars running. I always wanted an extension cord that would tell me that there is actually juice going to the block heater, letting me know that I actually successfully plugged it in despite the old rusty plug.
Then I discovered that a fellow that used to run a towing company in Northern Ontario has invented it and it is called "PlugRite".
It is not an extension cord but it goes either on the end of the extension cord, or you can leave it plugged right onto your block heater cord. When you plug it into an outlet, it tells you that there is actually juice in the outlet. When you plug it into the block heater, it tells you if there is actually current going to the heater. So now you know you are plugging in a live extension cord, or that the extension cord is not working. And you know when it is actually heating. You can even spot those little lights from the house window, in case you want to control the whole process from inside the house on that cold winter morning or just check on an automatic timer.
Think about it for a minute and you will find other uses for such a testimony light: roof de-icing cables, pipe heater cables, well water heater cable?.. Of course this gadget was hard to find in the stores, garages don't want to sell it because proper use of a block heater will double the life of your starting motor, as well as your battery. Apparently the automobile clubs don't want to sell it because starting cars represents a large part of the business of their towing partners. So eventually it disappeared and then someone who had a better marketing edge re-invented it and got it into Canadian Tire. It is called the "Plug Alive Block Heater/Outlet tester" and it sells for just $20.
Two more gadgets that you may be interested in to help you through the winter. An extension cord that lights up at the end to find it in the dark, and some kind of a weatherproof timer device to not waste energy all night long like mine from Aube Technologies. Both of these are available in hardware stores.