Can you post a photo please?
The sirens discussed here do NOT have a button on the front grill or do you mean you have to push the grill to get a sound out of it whilst activating it via ST? Are you able to meter the battery?
I have 8 of these and never ever had a single issue with any of them.
Another thing to keep in mind is that ST are constantly doing things in the cloud especially with the migration to the new app and infrastructure etc. so with something working from one moment to the next does not necessarily mean a hardware issue although in this case ‘pushing the front grill’ it probably is.
EDIT: Quick question; how would you even discover that pushing the front grill gave you a sound, come clean, did you drop it lol?