You've heard by now of the concertgoer whose iPhone alarm went off (and didn't stop) during a quiet point in the New York Philharmonic's performance of Mahler's Ninth Symphony two weeks ago.

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You’ve heard by now of the concertgoer whose iPhone alarm went off (and didn’t stop) during a quiet point in the New York Philharmonic’s performance of Mahler’s Ninth Symphony two weeks ago. The conductor stopped the musicians, fingered the culprit (who finally managed to silence the phone), and then started again.

But was the alarm the fault of the ticketholder? The individual, not named in a New York Times follow-up story, had been a BlackBerry owner and was given an iPhone by his employer the day before the concert.

Either he or someone demonstrating the phone to him set an alarm for a time he would know he needed none: He was an orchestra subscriber, and knew right where he’d be.

I’ve been involved in a debate for days on Twitter and on comment forums with those who think the gentleman was an idiot who should have read the manual before ever daring touch his phone, those who think all phones should be powered fully off (not just have the ringer silenced for calls) while attending performances, and those who think Apple’s operating system failed to give the owner enough warning.

I leave it to you to decide with which of those or other alternatives you agree. But forearmed is forewarned: I have found that many people are confused about the states in which an iPhone makes a squawk. Here’s a guide to shushing your iPhone.

Power it off. The best move to prevent any sound or vibration is to power off your iPhone. iOS has you hold down the On/Off button at the top of the device for a few seconds. A red slider appears on screen. Slide it to off, and the mobile device powers down.

iOS devices actually shut themselves off entirely when powered down. This may seem obvious. But some phones have a mode in which they are off, but still wake themselves to sound alarms. (On a phone, Off is really always a little bit on unless all power is exhausted in the battery.) Hold down the On/Off button for a few seconds to start the phone again.

Silence the ringer. What you perhaps think is the “mute” switch on the iPhone is actually called the Ring/Silent switch, and puts the device in either Ring or Silent mode. In Ring mode, all incoming call sounds, system alerts and reminder tones produce associated noises.

In Silent mode, none of those bother you — or those around you. What’s excluded from Silent mode? Alarms, games and audio from the music player or apps that play music.

You can control some of the behavior of ringtones and alerts through the Settings app, where you tap Sounds. Any audio that the Silent mode mutes may be changed here.

The Ringer and Alerts slider is misleading, as the icon at its far left, which appears to be a speaker with no volume, still produces a slight sound in Ring mode.

But you can turn off the sound for certain alerts by tapping the category, like Text Tone, and flicking to the top of the sound menu, where you can select None.

Vibrations also make a sort of sound. An iPhone vibrates with enough intensity to transmit the feeling through solid objects, like a theater seat. If the phone is lodged against a hard surface it can produce a loud buzzing sound.

The Sounds screen allows vibration to be turned off when the phone is set to Silent Mode, and to disable vibration alongside the ringtone and other alert sounds.

Set volume to zero. When listening to music or playing a game, you can press the Volume Down button until the sound is turned off entirely. This does not work when an alarm sounds: You can reduce the alarm’s sound only to a whisper, not to silence.

Choose None for alarm. In the Clock app in the Alarm view, you can set alarms to use no audio. Tap + to set an alarm or Edit to change an existing one. Tap the Sound item and flick all the way to the bottom, then tap None.

The alert appears only on screen. That won’t wake you up in the morning, so it’s only useful if you want the alarm to appear while you have the phone in front of you.

Check for an alarm. If there’s an active alarm waiting to go off in the future, iOS shows a tiny alarm clock icon at the upper right in the status bar near the battery icon. If you see one there, check the Clock app to make sure you didn’t set alarms you didn’t mean to.

Perhaps in a future release, Apple could tie in its Calendar app to alarm settings so that choosing to trigger one during an event you’re attending would warn you, “Do you really want an alarm to sound while you’re at the symphony?” Until then, run silent.

Glenn Fleishman writes the Practical Mac column for Personal Technology and about technology in general for The Seattle Times and other publications. Send questions to More columns at