The pinpointer is a single-function PDA with for one task: Pointing to the Nuclear Authentication Disk. It makes zero sense for the captain to keep this on their person since they already have the disk, so it's best to hand it off to someone on the security team. This will come in handy when you inevitably get murdered and someone needs to find your corpse.
Finer points of the pinpointer
The pinpointer will display four different icons based on the distance between itself and whatever it's pointing at.
A black dot in the center will indicate that the target is in the same tile as the pointer. Between 1 and 8 tiles away, you'll see a green arrow. 9 to 16 is a blue arrow and anything beyond 16 is a red arrow.
Alternate Functions
The Bomb Dot Com
Your friends in the Syndicate reverse-engineered the pinpointer. In addition to being useful for tracking down the disk, the Syndicate pinpointer will also locate the Syndicate shuttle once a nuclear device on the station proper has been activated. It will also show you how much time is left until annihilation if you inspect it.
OH FUCK WHERE'S THE AI?!
The AI is malf and you've breached the core, ready to deliver sweet carbon-based justice. But there's no AI! Luckily for you and the crew though, your rouge silicon friend is emitting the same radio signal as the disk, which means your pinpointer can be used to track down whichever APC the AI has moved into.