Door knockers are fixtures attached to the door of a home, designed to the knuckles of the people who might come knocking to save allowed. They consist of two parts, a plate that is attached to the door and an adjacent hinging piece, often a loop, which can be lifted and tapped against the plate. Door knockers can range in size from the tiny metal armatures, often with a peephole to see who is outside, that are suitable for apartments, to large, lavish displays with a brass lion's head which knocking ring.
Does your door needs a beater? If you already have a doorbell, door knockers may be unnecessary, but most people want a door knocker for its looks rather than its function, so it's really a matter of taste. Door knockers are usually metal for durability, but this can vary from the most common brass fitting in iron, tin and stainless steel.
You really will not be able to tell how your door knocker will sound until it is applied to your door, but take into account the composition of your door. Most houses have a hollow metal doors and a large sign with a huge beater will make booming echo as beaten. If you need a solid wooden door, this is less of an issue.
You can find door knockers to complement any interior. If your house is a mini-mansion, you can safely go for the noble look. The head of a lion, the brass ring, or a griffin, for example, would not go amiss. Think heraldic. On the other hand, if you live in a colonial era farmhouse, the head of a big lion is ridiculous. Go for a simple ring.
You can also use door knockers to announce your preferences or hobbies. Do you collect dragons? Attend meetings of Wizard of Oz or Star Trek fans? Believe in fairies? You may find that your particular door knockers eccentricity to proclaim the whole neighborhood.