During the Apollo 11 landing, a misconfiguration caused the guidance computer to activate the 1201 and 1202 program alarms, signifying that the computer was overloaded and dropping low-priority tasks. This was connected to the master alarm system to get the crew's attention; the alarms distracted the crew and may have contributed to the long hover time and marginal fuel state on that landing. In actuality the 1201 and 1202 errors were not extremely serious, though the uncertainty of their cause at the time was a big concern.

In November 1968, NASA engineer Bill Tindall wrote a delightful memo recommending against tying a low fuel warning to the master alarm precisely because it was an expected occurrence: "just at the most critical time in the most critical operation of a perfectly nominal lunar landing mission, the master alarm with all its lights, bells, and whistles will go off."

The film Apollo 13 portrays the master alarm as a red light with a loud repeating buzzer. Is that reasonably accurate? Would that buzzer have gone off during the 1201 and 1202 alarms during the Apollo 11 landing?


The Apollo Operations Handbook, Caution and Warning section, identifies the alarm tone as "a square wave that is alternately 750 cps and 2000 cps, changing at a rate of 2.5 times a second"

Perhaps someone can gen that up? It appears to me to be more like an alternating type sound rather than a buzzer. If the Shuttle copied this sound for its master alarm (likely), I've heard that one a bunch. It is indeed kind of a warbling sound that to me sounds like a French police car (at least as they are portrayed in American movies).

Edit: just found the Shuttle spec, and it's 400 Hz for .4 seconds, then 1024 Hz for 0.4 seconds. So roughly similar (alternating) but not the same.

Edit2: Russell Borogove synthesized 5 seconds of each alarm at this link. Very neat!

Edit3: The above information related to the Command Module C&W system, my error, since the question is really about the Lunar Module C&W system. That, in fact, seems to have been a buzzer, although not through a loudspeaker:

A malfunction also activates a 3-kc signal that provides a tone in the astronaut headsets and supplies the PCMTEA with a telemetry signal .

I got this from an incredible resource I just found: the Lunar Module Operations Handbook, 800 pages of Apollo-y goodness.

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    $\begingroup$ I wonder if the moviemakers used a buzzer because they thought it would sound too much like an 80s video game to use the real thing, or if they just picked a sound that seemed appropriate. tvtropes.org/pmwiki/pmwiki.php/Main/TheCoconutEffect $\endgroup$ – Russell Borogove Nov 8 '15 at 21:26
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    $\begingroup$ That's so horrible, was it supposed to wake them up from the dead? "Do you want to hear the most annoying sound in the world?" I would've broken a window to get rid of the air quickly. $\endgroup$ – LocalFluff Nov 8 '15 at 22:32
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    $\begingroup$ lol! Yes, it was supposed to get their attention! Their fingers got sore from stabbing the button in the sims to shut it off! $\endgroup$ – Organic Marble Nov 8 '15 at 22:33
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    $\begingroup$ It would, in fact, have been designed to awaken them. One of the original drivers for the 3-person Apollo crew was that they could sleep in shifts, but they quickly realized it was hard to sleep while other people were working in the close confines of the CM, and decided it was fine to all sleep at once; ground control would be watching the instrumentation and the alarm would wake them up if anything drastic happened. $\endgroup$ – Russell Borogove Nov 8 '15 at 22:47
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    $\begingroup$ Reading the next paragraph, it sounds like the "tone booster" was triggered by the master alarm light through a photocell. Wow, that sounds kludgey! $\endgroup$ – Organic Marble Nov 11 '15 at 15:36

I found these three active links on Sound Cloud:

Apollo Caution and Warning System- Master Alarm https://soundcloud.com/stefan-kramperth/05-nasa-apollo-caution-and

Apollo Command Module Master Alarm https://soundcloud.com/lambertstudios/apollo-command-module-master-alarm

Apollo 13 (1995) Master Alarm Sound Effect https://soundcloud.com/iam-agena/apollo-13-1995-master-alarm-sound-effect

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    $\begingroup$ very nice find! $\endgroup$ – Organic Marble Nov 29 '19 at 17:35

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