And in what circumstances would one use it? What does it do? Who does it call?

So many questions...

It's for old people who get stuck. Someone from the tenant or building will come and help you.

You've never been in a handicap toilet in the west?

I have - and I've never seen an emergency button in one.

Interesting. I've often seen emergency buttons in handicap toilets in the EU. Where are you?

New York. Used to live in Palo Alto and Toronto, and I've never seen emergency buttons in disabled washrooms in hose cities either. Perhaps it's an EU regulation?

Examples: http://wheelchairsteve.com/2014/emergency-cord-in-accessible...

Contrary to what he writes, I've seen them in a couple of places in the UK. I rarely use the accessible toilet though, typically only in small but modern offices where the only toilet is accessible, or on trains.

In the US, I've seen them in just about every toilet in a hospital or health care facility, but never anywhere else.