For this project I'm building a physical kill switch/intrusion detection system which will shut down or reset the NAS if it is tampered with. If paranoid mode is enabled this will cause it to lock the disks so that an attacker can't access the data, if paranoid mode is disabled the system can be brought back online and the disks unlocked automatically.
Yes I know this is a terrible idea, I know that if there's one thing worse than full disk encryption for unrecoverable data loss it's full disk encryption with sudden power loss. Shhh.
So the plan is to have a mercury switch that will detect movement of the case, and a micro switch which will detect when the side panel is removed. There will also be a hidden arm/disarm switch, because otherwise it's going to be a total pain in the arse. Now I know a little bit about electronics, but not a whole lot, so I'm not going to build this in to the power supply which would be a much more reliable option. Instead I'm going to connect it to either the power or reset switch connectors on the motherboard, as either way it will trigger a lock down of the disks if the system is in paranoid mode (for anyone unfamiliar with the previous project, when in paranoid mode the servers will ping each other every minute to see if they're still connected and lock the disks if they're not, so a reset or shutdown will trigger that).
Thanks a lot to @Th3Z0ne for helping me out with the plan, and thanks for this helpful diagram:
I'm still waiting on some of the parts to come from china, all I have so far are the relays, some wire, and a micro switch I stole from work. So for now I've just thrown something together to see how it will work and refine the plan.
For testing I have the vibration sensor connected to the relay board and that's powered off the 5V pins from a molex connector. This is enough to see how the vibration sensor will work. In the completed version the mercury switch (I'll explain why the vibration sensor is crap in a minute) and micro switch will be connected to the relay, the arm/disarm switch will be on the power side and the other side of the relay will connect to the motherboard power/reset pins.
The vibration sensor test revealed that the vibration sensor will not work. There are two problems; the first is that the sensor triggers too quickly, it might even be too quick that it won't register, so for it to work it would probably need a delay added as well. But the bigger problem is that when there is no movement the sensor will either be in an on or off state, as in what state it's in at rest is different every time. This makes it unusable for this project.
Here's a video which shows the problem:
I'm going to have to wait for more parts to arrive before I can continue with this project, or even further testing as it's nowhere near something I feel comfortable actually connecting to my server. Hopefully they get here in the next few days and I can complete this project before the end of the month. But for now we'll consider it a work in progress.