How to know when my smartphone is EOL? Long story short, I have been under the impression that my Samsung S5 had still been receiving security updates even though I was aware it wouldn't be getting any major Android updates. One Google search later, I find out that this is not the case. After some reading, I went on Samsung's page and found a list displaying what Samsung apparently plans to keep updates for.

What I don't understand is why I'm not being told that my phone is effectively a legacy device and is not being supported anymore.

It's one thing to lose out on Android updates but it's another thing to be missing critical security updates.

All vendors should be sending out some kind of message to outdated/unsupported phones, otherwise everyone will be under the stupid impression that they can keep the same phone forever and still be secure.

Is there some way to find out when my particular smartphone vendor effectively stops pushing out updates for a particular phone?

There's got to be something better than checking their crumby website every now and then.

Any leads?
The only way easy way to have a phone with current software is to buy from one of the 4 companies (Google, Honor/Huawei, OnePlus, Xiaomi) that bother to keep older devices up to date;

https://www.xda-developers.com/list-android-devices-project-treble-support/

so that the OS will notify you of updates when they are avalable.
You can double check by cross referencing the kernel version and android security patch level with

https://www.kernel.org/

https://source.android.com/security/bulletin

Lineageos is a nice alternative for unsupported phones but is not without  issues;

https://web.archive.org/web/20170517160235/https://cve.lineageos.org/