SimplePush. They have an API that is simple enough to call with a curl statement and the parameters of that call are used as a notification on your phone. As a developer, I use it for long running tasks that I want to be notified about.
You can even E2E encrypt the messages so nobody can tell when you pirate something download the next version of your favorite distro.
This, or something close to it, is sometimes called cluttering: https://en.wikipedia.org/wiki/Cluttering