Vampire power is power used by appliances or electronic devices after they are turned off. While many appliances do use vampire power, plugged in extension cords do not.
Some cords do suck vampire power even when nothing is plugged into them. Extension cords are an exception. Cell phone charger cords are an example of a cord that does draw power even when it is not plugged into the phone. One way to tell if a cord is using power is to touch the adapter where it plugs into the wall. If it is warm, it is likely using power.
According to the U.S. Department of Energy, vampire power accounts for 25 percent of the power used by home electronics. Also known as phantom power or standby power, this power is used by internal clocks and power sources in these devices, allowing them to turn on quickly and save data in memory.
While extension cords themselves do not draw vampire power, if an electronic device is plugged into the cord, it may draw power even when it is off. Additionally, there are fire hazards associated with the prolonged use of extension cords, so it is better to use them only temporarily.