They run a custom vendor-locked distro named QTS, so they're not really as easy to modify as a normal system, I don't think you can even install programs like that.
I'll definitely bookmark it though if I ever get around to building my own solution, thanks!
I don't know if it's a universal thing, I've never bothered to research further. On my several-year-old Oneplus phone (Android), if I single-press the power button, it mutes the ringer and vibrate but the call doesn't end or reject (I could still then go and answer or reject the call normally, it doesn't affect the user interface, just the ringer/vibrate). That's how I've been "rejecting" unknown calls for a long time. A simple, elegant solution that doesn't give the caller any hints.
I have no idea if it's a QNAP-wide issue, or just some specific models, I haven't bothered to do that much research. I'm guessing that the discs WOULD spin down if you have that option selected if they weren't constantly being pinged a couple times a minute. That constant pinging is the part I can't seem to track down.
An excerpt from a post I was reading while researching this sums it up prettt well: "700 posts about spindown/sleep/standby not working in the QNAP HDD Spin Down Forum. No one seems to be able to resolve it. Qnap clearly couldn't care less."
The only solution that I've found that seems to work is to install some other operating system on it, which kind of defeats the purpose of buying a turn-key NAS, and is slightly outside my comfort zone right now. I just ordered a kill-a-watt, so I'll see how much power it's taking with/without drives and go from there if it's worth my time to dive into an OS swap, or building a custom rig.
If you can figure out how to get a qnap to spin down its disks, please let me know lol. I've been searching for months and haven't found a reliable solution. I basically only need to access it once a day at MOST, so having the disks spinning away for like 99% of their life sucking down power is something I'd like to avoid. The problem seems to be that even with a perfectly clean slate, no services running, the system set up in their own RAID0 SSD pool, the HDD's, even with 0 bytes of data on them, are being pinged for access at least once a minute. I'm assuming it's some log being written to, but it's not anything visible in the file system, and I haven't been able to find any solution online, lots of people seem to have the same issue.
I'm tempted more and more every day to just grab one of those low-power embedded ITX boards and build up a custom rig. Other than the disk spinning constantly, the TS-462 does everything I need perfectly.
That solidifies my suspicion that it's a standard Android feature... I also don't get many spam calls, and only distinctly remember performing that action on this most recent phone.
Based on OP's comment "...I always assume that rejecting the call outright will also be detected as a deliberate action and therefore a person is on the other side...", I figured maybe they didn't know about that feature and/or have an iPhone and they somehow don't behave that way.
I also miss the old days of Android... I got a smartphone specifically to play Pokemon go in 2016 lol, up until that point I was still rocking one of those Casio Gzone indestructible flip-phones. Walked into WalMart, bought the cheapest LG whatever phone I could find (Android 5 I think?), caught a bazillion Pokemon. I remember buying multiple batteries for longer sessions, because you could just pop the back off and replace it on the go.