[PhantomGremlin]

Just clicking multiple times will bring up wallet, siri, or do nothing.

On my iPhone 13, just now, I rapidly clicked the power button 5x.

The phone immediately made a loud sound and put up a screen that said "Emergency SOS". There was an option to "cancel" it, but I assume that the phone would have contacted 911 in short order unless I quickly cancelled.

So the correct description is probably "it depends".

[breser]

There is an option in the settings to make it not actually call unless you press a further UI button on the iPhone.

In Settings go to Emergency SOS. Uncheck Auto Call

[mypalmike]

My Android phone did exactly the same. Very loudly and unexpectedly.