A great example of usability engineering is right in front of us every day (especially as we become a more technological society): electrical outlets!
What a simple fix to ensure that electrical plugs are inserted properly into the electrical outlets – don’t give the user any other choice! The manufacturers can control the safety of their products by giving their users only one option.
Interestingly enough, keying would be one good way of controlling the accessories to medical devices. They keyed accessories would be the only accessories to be used with the device, giving the manufacturer assurance and greater control of the device as a system. Of course, the manufacturer would also have to be sensitive to its market as well. What good does a keyed accessory do if none of the devices sell because of a restriction on the type of accessories available for use?