Yes AFAIK, so long as you can remember all these numbers while your blood is spraying the walls (or whatever):
112 for emergency assistance from an ambulance or the firefighters (gratis in all European countries for urgent help)
101 for emergency assistance from the police
1722 in case of a storm or flooding when you need assistance from the fire brigade
1733 for the doctor on duty (non-urgent)
The app relieves people of having to remember those numbers. I’ve heard 911 is so commonly known from hollywood films that it has been made to work outside the US in some regions, but I’m not sure about Belgium. Looks like those numbers have to be remembered because of their differences (911 covers police+fire+medics).
The app works both over internet and over GSM. If you cannot speak for some reason¹, the app transmits a variety of useful info about you. There may also be situations in rural areas that don’t have GSM coverage but where wifi is reachable (not sure). Note as well foreigners visiting Belgium could have a CDMA-based smartphone in which case wifi would work but not GSM.
What I don’t know: 112 is obviously toll free, but does it work when you have no GSM subscription? In some parts of the world you can dial for help without a functional subscription but I’m not sure if that is universal.
reasons you cannot speak could be physical (choking), or if you are being attacked or hiding from an attacker maybe you need to silently signal.