You eventually start asking the questions that really count.

I have never in my whole life met a single microwave that did not beep once the set time was up. Each and every one of them has beeped loudly and obnoxiously. The earliest microwave I can remember, one that my dad brought from abroad in the beginning of the nineties (at a time when microwaves in our neighbourhood were generally unheard of) happily emitted three loud beeps in rapid succession. Several decades later, I still have very clear memories of that sound. It was intrusive, artificial and foreign. The sound simply did not belong in that bygone world, yet to be littered with ever-present semi-autonomous devices that humanity has since gotten so used to sharing its living spaces with. Of course, it is only in hindsight that I realize this.

Since then, I have come across microwave ovens that emitted four, five, … up to eight beeps! Each and every time you used them. This feature is apparently non-negotiable. You cannot turn it off, not even on those models with user interfaces resembling the control panel of an Apollo cabin.1 I suspect that beeping must be part of the core interface contract of a microwave. You trigger it, it does stuff,2 and finally emits loud beeps. Hence, it’s a microwave.

But it usually does not end there. If you did not manage to swiftly attend to the beeps, the device starts the beeping all over again (usually after a mere thirty seconds), and this goes on for a while, perhaps indefinitely. Like a small child switching into tantrum mode due to lack of immediate attention. Microwaves do this despite the fact that heating itself is automatically cut off just before the beeping starts, so there is no hazard whatsoever in ignoring the device in its present state. Apart from having to endure the annoying beeps.

Contrast this with regular kitchen ovens: you set a temperature, and perhaps some heating mode (at least on fancier models) by selecting the heaters below or above the cavity (or both), possibly with forced circulation. Or maybe you activate the extra grill heater. You most probably do not set a timeout on the operation of the oven.3 You just let it run, inspecting the contents of your bakeware from time to time, and/or keeping an eye on the kitchen’s (most literally) wall clock to turn it off at some point. The same goes for stoves, despite the fact that most domestic cooking activities use them (so they carry most of the associated risk).

Getting distracted, forgetting one’s oven is on and going about one’s business (perhaps even leaving home) has historically been a frequent root cause of major accidents (house burning down, etc). Somehow this did not force manufacturers to equip their devices with countdown timers and non-negotiable beepers or ringers to alert on the timeout, nor did it force the hands of regulators to demand such a feature from the manufacturers. To this day, you are still free to forget your stove silently overheating a frying pan with plenty of cooking oil in it, quietly heading towards combustion temperature, on its way to ignite and burn down your entire house.

So what is the problem with a little beeping, you might ask?

Well, here is my breakdown of the entire universe of possible use cases.

  1. I am trying to warm up my cup of tea. I want to drink warm tea now. So, I am literally standing in front of the device, watching the seconds count down as the microwave is humming away. When it’s ready, I immediately remove my cup. I will do this regardless of whether there was a beep at the end or not.4

  2. I am defrosting, which will take half an hour or more, on a low power level. I will definitely not keep standing there in front of the device. When the time is up, I will probably get caught in the middle of doing something else (like peeling and cutting onions or potatoes, or whatever else that makes my hands literally dirty so I do not want to touch anything before washing them and wiping them dry – or worse, perhaps I am in the middle of a train of thought sitting in front of a piece of code). The beeping does not really make me attend to the microwave any quicker; I will have checked it out anyway when I got to it (or needed its contents, or needed it to warm up something else). The only effect of the beeps is that I am now frustrated and angry at the device that will not leave me alone.

  3. I am warming up some food but it’s not very urgent. See, I’m warming it because it has already gotten cold (maybe I was about to have lunch, but I got a non-maskable interrupt, and now my lunch is cold). Warming it up an additional time is no big deal. If I have something more urgent than consuming my just-warmed-up lunch, it is very likely that an obnoxiously beeping microwave oven will not improve things.

On a more abstract level, notice that the task of the microwave is either a high-priority foreground task (subject to continuous human attention) or a low priority background task (while the human is predictably occupied with something more important). And it is not for the microwave to decide which of these is true in any given case. But even more importantly, in any case, beeping is unnecessary, annoying, or both.

With the above in mind, I have a couple theories to answer the original question of Why Microwaves Beep:

  1. Whoever made the first microwave thought the beep was a good idea. This is forgivable given how much of a novelty it was at the time. It was probably the center of attention every time it was started, hence the beeping was not perceived as interrupting anything more important. What I cannot fathom is how, in the span of many decades, no product designer dared to re-evaluate the necessity of this behaviour.

  2. This is a feature that “looks good on paper.” The product managers and marketers probably feel that this is something users actually want. Or something they must provide to be competitive. It is hard to justify taking away features!

  3. People do not mind the beeping, because they are so accustomed to electronic devices in their surroundings that they do not (fully) control. Lately, this dilution of expectations has gotten much worse with smartphones, which the average owner has very little control over.5

  4. Given that microwave user interfaces are invariably terrible, and that people usually select their device based on other criteria (such as dimensions, power capacity, brand, etc), competition on the “free market” does not naturally cater to this problem.

  5. Since there are no “open source” microwaves, users are not empowered to change the status quo, thus they are trained to accept the constant beeping as an inherent part of the “microwave experience.”6

Speaking of the lack of open source solutions, I have a binary patch to apply to this microwave of mine… in the form of a pair of pliers!

Oh, now that we’re on topic, I will just bring this up in closing: Why do microwaves have clocks? That is, why do they all have to show a comically inaccurate, non-auto-adjusted, continuously drifting, bad approximation of the time of day? Of course I cannot turn it off on mine, even though I have a real wall clock that displays the correct time, at least within a margin of error much smaller than what I can possibly notice as a human. Accurate time-keeping is a solved problem, but microwaves are so notoriously bad at it… why bother?

1 Totally out of scope for this post, but a fine test of “tech sense” is this: upon close encounter with a previously unknown microwave device, how quickly can you get it to warm up your cup of tea? Trying to do this on one occasion, I got lost in a menu for setting the mass, temperature and tissue composition (bone/meat percentage) of the thing I stuffed into it. I had to realize this was a nasty trap, and admitted defeat. A microwave, unlike emacs, is mostly used by unsophisticated users, and, unlike emacs, cannot afford to be openly hostile towards noobs.

2 It is customary for microwave ovens to not warm your food. Well, maybe it will have gotten warm here and there, but not properly and evenly. Invading aliens could well argue that warming food is not part of the core functions of a microwave oven.

3 Today there might well exist some really fancy models where this is no longer the case, but it has been true historically.

4 You bet there was! Now my ears are ringing, as I was standing too close.

5 If you think you have control over your own smartphone, I dare you to uninstall all the applications you never use. All of them, no excuses. If you do not recognize it, remove it. (Oh, but you can’t? Did you say you control the device?)

6 I remember a time when people accepted that their desktop operating systems will spontaneously crash as a natural part of their working days. People quickly learned (and were advised) to save their work frequently, and everyone moved on with their lives. The revolution came from elsewhere.