This is to ensure that if the driver / conductor is incapacitated the train will still come to a halt. And that in turn is because runaway trains have happened.
For logner tunnels etc there is an override, where emergency break doesn't break immediately as stopping a train mid-tunnel is most of the time the worst choice. Smoke in tunnel is dangerous. Emergency help can't reach it. Evacuation has confined space. etc. There emergency break rings an alarm with the engineer. If they ignore it, it will stop after a while, but usually they will use intercomm to understand the reason.
A way however you can stop trains on a German train line is by putting a 2kHz electromagnet on the tracks. That will tell the train that it just crossed a red signal and will stop.
Crusade against Wikipedia that the information is stupendously risky if you think that's a good use of your time.
https://eur-lex.europa.eu/legal-content/EN/TXT/PDF/?uri=OJ:L...
(p. L 342/109-110, or ^F RADIOSTOP)
This is Official Journal, available in all EU languages (at the time).
Also the risk is .... not existent. To damage railway infrastructure there are way more efficient and simple ways (getting a rail to derail, destroy some signaling cables, ...)
The "attack" here would require quite some investment in equipment (power etc.) and only bring a single train to a realtively quick stop, well in safe margins, where the driver after a quick check with the dispatcher can override and continue the ride, while investigators would collect the equipment.
It's impractical for a stunt (way simpler and more effective: just walk close to the tracks and they will do emergency stops for all trains close by) and ineffective for an attack.
That’s false, at least on modern trains, in France, for what I know.
Any modern train will not stop when you pull the alarm lever.
The first thing that will happen is that you will be in communication with the conductor, then the train will be stopped in only two scenarios : either you are communicating a real emergency or you don’t respond at all to the conductor asking you what happens after a given delay (which IIRC is 10 seconds).
And fwiw, a friend of mine who is conductor explained to me that if you activate the alarm lever by inadvertence, the worst thing you can do is to not answer by fear of having problems. If you say it’s an error, the conductor will just ignore it and continue its day while if you say nothing, the conductor is forced to emergency brake the train and all the trains on the line.