Wristcoms are electronic wireless communications devices worn by residents of the Centauri Princess on their wrists, which play a number of different roles essential to their livelihoods.
They are much like a modern day wrist watch in appearance, encompassing a metallic case with a small screen that is strapped around one's wrist with a bracelet.
Wristcoms perform multiple tasks, ranging from 2-way video comms to acting as a tagging device for surveillance of prisoners, to serving as a miniature laser weapon for self defence against threats from dangerous animals. They are also used as credit cards in paying for goods and services. Since they are wirelessly networked to the broader IT infrastructure and CPC, wristcoms automatically adjust one's bank account with debits and credits, after each transaction. This is exemplified in Chapter 3 of First Ark to Alpha Centauri when Alcyone needed to pay for her dress in Joanna's fashion store.
Wristcoms are also useful to visually signal and identify one's position across the curving landscape, when communicating with someone. The exotic landscape of the interior means that two places are constantly in sight of each other in about 80% of the time. There is a very interesting and compelling example of this on page 58 of First Ark to Alpha Centauri, where on this particular Sunday afternoon Alcyone is visiting the cemetery and Joey is with Yurchenko on the edge of the Black Forest, both diametrically opposite one another across the cylindrical interior. Joey then flashes his wristcom to Alcyone, and vice versa, to show where each of them is. They then each see the other's position on the landscape as a "silver glow" cast directly overhead by the laser function of the wristcom.