COMP

This is concept art of the COMP. For those that don't know, the COMP is a personal computer in the Shin Megami Tensei series. Loaded with the Demon Summoning Program, it is what allows the protagonists to summon demons.
In Persona Zero, they are common sights in the arm of... Well, most people. They're like smartphones, the latest craze. The protagonists will use modified COMPs, which will have an slot with which to insert their Persona Cards, which will cause the COMP to aid in the summoning process. All of them also have a detachable wire, which loops around the head and connects to a headset, allowing the mission control to keep in contact. attatching to the headset is a pair of prisim spectacles, which prevent the characters from getting disorientated inside the dungeons. The hero's COMP has a dealer attachment, allowing him to store several Persona Cards, and switch between them during battle. His also has a Fusion Spell Program, allowing him to execute Fusion Spells on his own, like the Protagonist of Persona 3.
In colour, they are silver as default, with a highlight colour varying on the taste of the user. The colour of the fibre-optic wire and the lenses of the spectacles match the highlight colour of the COMP.

There is a faint glance at the hero in the above image as well, as the figure modelling the COMP and battle attachment.