Electric Blankets are generally safe, and of course, warm and comfy.
Do inspect them now and then, to make sure nothing is frayed or breaking, and consider replacing your blanket if it is more than 10 years old – very rarely, broken electric blankets have been known to cause burns and fires.
Don’t use an electric blanket if you are diabetic, or have a medical condition that makes you less sensitive to pain/temperature change. Electric blankets can be dangerous to people who can’t tell when they overheat.
Also, consider not using an electric blanket if you are in the first trimester of pregnancy. One study found that electric blankets increase the chances of miscarriage (very slightly).