>>6171457<span class="mu-s">First, regarding the AR systems, vents, and such-like</span>. I've noted systems displaying themselves on your feed, but it's always possible to Sense around and scan for other, more hidden systems (some run in stealth mode so not just any two-bit hacker can access them).
When you have access, link or line to an INTERFACE, it allows you to take action in the physical world. Usually, the closer your actual target is, the better, and it depends a bit on the specifications of the system itself - though usually, you can accomplish quite a lot of HARASSMENT, change the local conditions, assist others and such-like. It's worth keeping in mind, especially for distractions, guiding, operations or teamwork.
