Smartphone / Tricorder
A link is a gadget somewhat like a smartphone. Most have multiple methods of wireless transmission and are capable of recording through a variety of sensors. It can be assumed that a person always has a device of this nature on their person at all times.
Form and function vary widely by make and model. Simple versions are commonly worn as jewelry or badges, but they can be purchased (or printed) to virtually any specifications. Additional functions may necessitate larger and bulkier builds. Handheld, belt-worn, and even backpack sized links are common.
Inconvenient sizes or awkward shapes account for abilities granted. Some may have something akin to cartridges, clips, or battery packs. A robust link with many scanning capability approaches tricorder size if the range is relatively limited. Minimalist varieties will often be found sewn into clothing or garments.