@tamaaya I'd just done it before posting my reply to make sure it was still the case that this still worked because I'd not done the 5 button press for a long while. No loud noise from my phone (and I also can't recall it making one in the past, either). Admittedly, it isn't something I try out very often.
@JonnyT Yeah I just checked as well. I'm pretty sure you have to hold the button down or something for the alarm to sound. I've definitely triggered it by accident when diagnosing phone problems at work.