"Idle hands are the devil's tools" says that people (especially children) are more likely to get into trouble when they feel bored and have nothing to do. Example: "My mother taught me that children should always be kept busy; idle hands are the devil's tools!" The "Devil" (in the Christian bible) is the bad angel who fights against God by getting people to do bad things. The Devil uses whatever tools are available. "Idle hands" are the hands of a person who is not doing anything. "Idle hands are the devil's tools" because when you are not busy you may end up doing things which you should not do. Example: "It makes me nervous to see those kids outside just standing around; idle hands are the devils tools!" Hands often represent action, but idle hands are hands that are not acting; they are waiting and looking for something to do. "Idle hands are the devil's tools" says that when people are idle they will find things to do which they should not do. Example: "I'd like you to keep the kids very busy while we are gone; they get into trouble easily and idle hands are the devil's tools."