eli5: If most electronic appliances' efficiency losses are through heat, does that mean that electric heaters are 100% efficient?

Edit:

Many thanks for your input everyone!

Just to clarify, I don't want to take into account the method of generating electricity or shipping it to the home, or the relative costs of gas and electricity. I just want to look at the heater itself! i.e. does 1500W of input into a heater produce 1500W of heat, for example? Or are there other losses I haven't thought of. Heat pumps are off-topic.