Direct Neural Interfaces are the process of extending a user’s neural commands onto a generic system that can then be used to control arbitrary electronic devices. Basically, you think it, and the machine does it. What’s not to like about that?
Note that although many cyberware systems - for example, replacement limbs - are controlled via neural shunts, they do not count as DNI. They have their own bespoke cabling into your nervous system. However, in some circumstances, having DNI can help two systems that would otherwise conflict interact more harmoniously, for example Wired Reflexes and Reaction Enhancers.
In game terms: replace all “wireless bonuses” with “DNI bonuses.” DNI bonuses apply whenever the character has a direct neural interface connection to the item of gear, and hence can control its full funtionality via mental commands. You do not need to maintain any access to the wider Matrix to use them, but you do need either a wired or a wireless connections between the devices and your datajack.
In real world analogy terms, think of DNI as being like USB combined with Bluetooth, with one end plugged directly into your brain. Just about anything you own can hook into it and work with anything else, and your brain can command anything hooked into it.
There are two main ways to handle the interface between your gear and your brain matter:
More than half the population have datajacks fitted, and if you exclude the SINless poor that rises to more than 75%. They are cheap and common.
Several items of common cyberware include a datajack for free:
Your datajack can connect to stuff over a wired connection or a local wireless one. Both offer the user equivalent levels of control over their gear. Wireless, however, has the risk of getting hacked. Wireless devices can be targeted by hostile deckers with a variety of offensive Matrix actions.
In game terms, these are largely interchangeable, and you get any DNI bonuses whether you use wired or wireless connections. However, it can require an extra Simple Action to plug cables in if you want to avoid wireless.