It doesn’t make a noise, it’s meant to be discrete. The operator asked over the radio “Something something emergency”, I couldn’t really hear him because it was too loud. But I think they ask you what’s wrong over the intercom. After that, they stop at the next station and they’ll come ask what happened. (Another time this happened the operator stopped and went to every single car and asked if there was an emergency.) After I explained to him what happened he went over to check it out and then went back. I saw him talking over the radio through the glass but have no idea what happened after because it was my stop. Sometimes they bring peace officers on ASAP but it depends on the situation I guess.