What are the types of AAC systems?

When children or adults cannot use speech to communicate effectively in all situations, there are options.
Unaided communication systems- rely on the user's body to convey messages. Examples include gestures, body language, and/or sign language.
Aided communication systems -require the use of tools or equipment in addition to the user's body. Aided communication methods can range from paper and pencil to communication books or boards to devices that produce voice output (speech generating devices or SGD's)and/or written output. Electronic communication aids allow the user to use picture symbols, letters, and/or words and phrases to create messages. Some devices can be programmed to produce different spoken languages.