One of the MacBook keys can become a mouse

Apple is developing a keyboard for a MacBook laptop with a removable key that can be used as a computer mouse. 

This development is described in an Apple patent registered with the US Patent and Trademark Office (USPTO). 

The documentation describes a standard MacBook scissor keyboard with a hidden, removable key. This key will contain the position sensor. Apple describes the system as providing "convenient, portable, and accurate input."

The documentation explains that for some tasks, such as graphic design, computer-aided design and modeling, and editing large and complex documents, a portable mouse is more appropriate than a trackpad. Apple acknowledges that carrying a separate mouse can be cumbersome and "redundant". 

According to Apple, such a removable key is a viable solution to this problem. Some embodiments describe a key with a built-in battery that could function as a standard keypad button if needed. 

Of course, the fact of registration of the patent does not at all indicate that Apple will bring the development to a commercial-stage.