This is a weaker, less intrusive version of Alexandra’s brain implant, allowing the person to mentally communicate with whoever Lumina connects them to.
If the person allows her, Lumina can also read their thoughts, sensations, and feelings, as well as let them experience any kind of simulated or forwarded sensations.
It basically gives the person a direct connection point to Lumina’s network, and by that Alexandra, without becoming too intrusive.
Elizabeth will eventually receive such a brain link implant, allowing her to connect with Alexandra and Lumina on a far more intimate and fundamental level.