Well, I have not played the latest version (only up to Chapter 2 and it was more than 6 months ago), but if I remembered it correctly, the facility USED to be a top-secret facility because Kindra's late father and mother were contracted by the military, but it was no longer the case (sometimes) after the demise of her parents. Since Kindra lives in seclusion and very private person (also I have kinda vague memory of this), the facility is not known to anyone or had visitors for a long time, so I guess security is not a concern? Anyway, that's how I interpreted the scenario. As long as there were no prior scenes describing how the security in the facility works but the suddenly failed when there is an intruder, I think it is still believable (that there was no tight/high security system in place). Cheers.
Security measures don't just go away, they don't expire. Yes you may not have actual live human security guards, but all the security tech is still there.
Here is an example, where I live, gun shops are required to have back-to-base alarms that trigger not only their security company but also the police.
One I did work for had their alarm triggered because it hadn't been disarmed before the door was opened and the police arrived in under 4 minutes.
Secondly, not only does this place have secret projects, weapons manufacturing capability and a lot of secret designs/tech .etc it also has dangerous chemicals [we were told about this when June came to work in the lab] in an R&D lab which means there are certain requirements by law that must be adhered to as far as safe storage and security measures to keep them from being taken out of the lab or stolen.
In systems I've designed not only are there cameras, door sensors and the like, there was also an atmospheric pressure sensor, to detect if the room pressure had a rapid [outside of a set limit] change by the opening of a door, window or other breach.
There were microwave motion detectors, very sensitive. There should be not real motion inside a locked room, these things not only detect motion, they determine speed and can even detect people crawling or sliding along the floor and on top of that they can log direction of travel too.
Then there were acoustic sensors, what would happen is the base-line ambient sound would be calibrated so then if the system is armed and noise beyond the base-line is detected that also triggers the security response.
There is more but I won't make this any longer than needed, the point being that security systems are done in layers and employing human guards is just one of those layers and in the situation we have in Artemis all the non-human security systems would still be in place, it would be essentially impossible to breach undetected and then to get in, find your way around, find what you are looking for and exfiltrate with the stolen items? It isn't happening with 1 day of prep by one or two guys.