This is a short one.
On my main phone, I have been blocking Google Play Services from network access (using Netguard).
Unfortunately, this has the side-effect of making Signal stop receiving messages in the background – I’d only see messages once I opened the app. Annoyed the heck out of my wife and kids, and it got to the point that I really could not justify my stance on privacy/security in the face of this.
And yet, everywhere I read, people said Signal works fine even without Play Services – it will do its own polling in that case.
So what was the problem? My first “duh!” moment was realising that blocking Play Services is not something that Signal can detect – how would it know? I don’t know enough about the innards of Android to be able to answer this question but it seemed like a reasonable guess.
So I disabled Play Services.
Still no luck.
Then I reinstalled the app.
Still no luck.
It turns out that you need to uninstall Signal (after taking a backup, and making a note of the 30-digit key the app creates for the backup), then reinstall it while Play Services is disabled.
In other words, Signal only changes its behaviour based on the state of Play Services at the time it is freshly installed!
Oh well, took me a while to get there.
The things I do for my wife and kids… ;-)