Keys have changed little over the last 155 years. Essentially, a key is a small credential that is easy to use and unobtrusive during everyday life.
From time to time key design has changed from the bit keys (they often look like a flag) to paracentric keys to modern security keys. The term “High Security” is an insurance term used to describe a type of key and lock that meet the insurance industry’s requirements to reduce the amount of money they need to pay out for claims. An important part of those requirements is the integrity of the key used to open the lock.
The lock industry has responded to this requirement by utilizing the patent system to protect the blank key needed to make a duplicate. Blanks are only available from the manufacturer, through a tightly controlled dealer network, to the end user. Third party key manufactures cannot create the blanks for high security locks without risking a lawsuit.
Once the patent on the key blank expires the manufacturer is under pressure to improve the key to secure a new patent. This happens every 15 to 20 years.
Mul-T-Lock often uses common sense when designing their locks. They have found a way to create a new backwards compatible key that extends the patent protection of their Interactive locks an additional 20 years. Called the Interactive+, a small change in the shape of a moving part in the key means that the older, out of patent, keys will not work in the new locks but the new, patent protected keys will work in the old locks.