Yes it can.

The fob has no idea what it has access to, in most systems it just has a serial number. When you tap it on the reader, the reader scans its serial number. The system has a list of which key numbers are allowed to open which doors at which times, if your key matches it opens the door. These almost always have some kind of log of which key opened which door when. Whether the building management knows how to access that is anyone’s guess.

If he loves in a building with fobs there’s probably cameras also.

So if he’s worried about after the fact investigation into his movements, he should live somewhere else.

Yes. the system logs every entry/exit by keyfob.

Whether the building managers associate those fobs with individuals or even know how to look at the log is a different discussion entirely.

That said: If the building cares enough to have a lock on the door then they have a camera too and THAT is much more likely to be recorded. So if your “friend” depends on people not knowing he is entering or exiting his building for whatever reason… good luck with that.

Fun story time: I used to work at a facility that was VERY strict about people badging in and even out of many areas. At one point it came up in a safety debrief that there was no way to log who was inside or outside of an area… that required badging in and out. Could see someone’s brain cell trigger in real time as they proceeded to ask a lot of very pointed questions that boiled down to:

They had an access control list that was checked. They did not know how to access the log files to know when that list was checked or even the result of a check. The person who asked questions was pushed out of the company because it was easier.

Generally the key fobs have a circuit and antenna inside and the circuit has a code that it broadcasts when it is near the transceiver. Some systems are more complex, but at the lowest level the system disrupts a magnetic field around the transceiver in a certain way to generate the code or is powered up by the transceiver and transmits the code using that power. That way no battery is required and it can fit inside a thin card or fob. Some older ones have a very small battery to increase range or create a more complex or modifiable code or for proximity use rather than touch.

That code is then authorized or not to open the door in the security system. And yes every time the fob is used, it is logged. And depending on if the fob has a battery, it is possible it tracks leaving. If they don’t have to touch the fob to a panel and just need to have it on them, then it logs any time they approach the door regardless of entering or leaving. If it requires touching or bringing it close to a panel and they don’t have to do that when leaving then it probably doesn’t log them by proximity.

Whether or not the log has the person’s name or just the code or ID of the fob depends on how old or cheap the system is. But there’s definitely some document somewhere that lists the peoples’ names and which fob they were assigned if it’s not in the system. So it’s easy enough to find out.

Any system that has the same code in every fob would be either super old or super cheap and unlikely to be used on secure doors. Having unique codes means that if a fob is lost or stolen it can be deactivated among other things. Which is a no-brainer for security if there is no real significant cost. The only reason older systems didn’t is because the tech couldn’t create long enough codes on the circuits that existed. And super cheap systems don’t want to create too many different codes since it’s cheaper to mass produce the same one over and over. Basically why car fobs can often open other people’s cars. Either they’re old or the car company’s too cheap and it’s not their security at risk, so they don’t care.

The system almost certainly will record every usage of the keyfob. It may also record opening the door from inside.

Does this key fob log every entry/exit?

Entirely depends on how the reader system is setup and configured. It’s likely, but not a guarantee.

He’s cautious with cell phones and leaves them at home, but wonders if the key fob could potentially cause problems.

They’re a passive, no power system. They require energy from the reader to function. They’re not exactly GPS trackers, but maybe someone somewhere has figured out a way to track them.

Depends on how they have set it up but in the ideal it will have be individually linked to a user. Iv heard of cheep complex managers just setting each fob to the same internal id. Meaning you can’t deactivate a fob or track the users. If anything it would be the same as CCTV on the lobby and public spaces of a complex. I would doubt that you would need it to exit as most doors need to let you out without resistance. This is possibly a fight between security and privacy. The other residence in the complex are more concerned with unwanted entries.