Think about a product that may not be top of mind, but you interact with on a daily basis: your toothbrush. Ask yourself the following questions: Does it work? Can you use it as is? When it was new, could you use it without any instructions? And does your toothbrush give you unexpected delight? Most likely the answer to the first three questions are yes, and the last one has you scratching your head on how a toothbrush (not the toothpaste or any related products) can offer “unexpected delight.”

This is the challenge of a designer – How to design delightful interaction into a product. 

Interaction is defined as shaping products for people’s use. The interaction hierarchy goes like this: Functional –> Usable –> Intuitive –> Engaging

The first level is functionality.  Does the product accomplish the job? This must be met at a minimum. Otherwise, why should the product exist? In our toothbrush example this would be the ability of the product to brush teeth.

Second, usability - Is the product usable by the intended person? Will someone use the product way the product is intended to be used? Does it need assistance, another person, or another product to accomplish the task? Can you use the toothbrush? Or does it need multiple people? Another product?

The next level of interaction is intuitiveness: Can the product be used without significant instruction? Does the product just “make sense?”

To be engaging: Does the product draw you in and give you unexpected delight? Does it do something that seems so natural, yet you did not think the product could do that? This is engaging interaction.

If you are still wondering how a toothbrush can be engaging, take a look at this:

The designers started with a functional aspect, rinsing after brushing, and then figured out a way to incorporates that feature into the design of the brush. While many other companies are changing shapes, colors, and bristles, these designers found a way to delight with added functionality. In the process of doing so, they also removed a pet peeve of mine: that plastic handle which could be re-used for a longer life than the bristles last.

Want to take your designs to the next level of interaction? Take a look at these resources:

• Philippe Starck on Design at TED
• Interaction Design Association
• Designing Interactions