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In my fantasy story, it has come to a point in which it is completely necessary for lead to wake up at a certain time that his body is not accustomed to, however, this made me stop. It is crucial that no other character or person wakes him up, so how would he? The system of time they have in this world is similar to sun dials, being specially colored glass panes in a window that will display different combination of colors according to the time. So, I would like this alarm clock to somehow connect to this system? The twist is, he needs to wake up at a time in the night. These dials still do work during the moon's influence, but not as strong, of course. Note that this society has the technology equivalent to that of Imperial China at its height, but for the sake of the story I would like to avoid gunpowder or other combustible elements.

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    $\begingroup$ Drink a couple extra glasses of water. $\endgroup$ – user535733 Nov 13 '17 at 20:33
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    $\begingroup$ 2 apparent options: First - don't go to sleep. Second, do what user535733 said and drink extra water :) $\endgroup$ – NotMe Nov 13 '17 at 20:40
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    $\begingroup$ @NotMe He needs to wake up at a specific time, so drinking extra water would be to unpredictable. And it is necessary that he does go to sleep. $\endgroup$ – Unhappymarshmellow Nov 13 '17 at 20:42
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    $\begingroup$ roosters. just saying $\endgroup$ – Fleon_ Nov 13 '17 at 22:13
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    $\begingroup$ So ... no candle burns through a cable holding an anvil over a dragon's tail, anvil's drop provoking dragon-fire heating up a boiler feeding a steam-whistle then? Bummer... I guess Rube McGoldberg of the Clan McGoldberg is still awaiting his hour of glory. $\endgroup$ – akaioi Nov 13 '17 at 23:08

16 Answers 16

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He needs a Clepsydra (https://en.wikipedia.org/wiki/Water_clock). Basically, a reservoir filled with water, with a puncture through which water flows at a constant rate.

These clocks have been well known for millennia, so they are available to your character.

Upon emptying the reservoir, your alarm would be triggered.

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  • $\begingroup$ Good answer, but if possible I would like it to relate to the sun dial. $\endgroup$ – Unhappymarshmellow Nov 13 '17 at 21:00
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    $\begingroup$ @Unhappymarshmellow what do you want? A moon dial? $\endgroup$ – kaine Nov 13 '17 at 21:57
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    $\begingroup$ @Unhappymarshmellow I don't get it. You want something linked to a sundial that works when it's dark? Sundials intrinsically don't work when it's dark. $\endgroup$ – David Richerby Nov 14 '17 at 16:05
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    $\begingroup$ @Unhappymarshmellow you use the sundial to work out how much water to put into the reservoir. That's your link. $\endgroup$ – Baldrickk Nov 15 '17 at 12:58
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    $\begingroup$ @Unhappymarshmellow you can't always get what you want, but if you try sometime, you just might find you get what you need. In this case, you need... a water clock. $\endgroup$ – RonJohn Nov 15 '17 at 15:13
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Here is a little 2 part mechanism that might work (though it's a stretch)

As part of the sundial, place small panes that are lenses. My brain has concocted a mental image of the cathedral with a huge stained glass sundial. There are lens panels that have been fixed in place for centuries, their focal lengths known, positions marked, and candle stands at specific heights so that the holy sunlight ignites the candles every day. Maybe matches are forbidden in the temple. The lenses will only be aligned for a few minutes each, but with enough time to light a candle wick.

Then place a Candle Clock, un-lit, with the wick at the focal point for a given time of day when the sun is out. Our hero uses this to ignite the candle clock, then he goes to sleep.

At the marking for the time your hero wants to get up, have the hero insert some sort of steel pin in to the candle. When the candle burns down to that point, the pin falls out, possibly onto some sort of noisy object like a thin steel pie pan. Multiple pins might be used to create a bigger cacophony, or further down, like a snooze.

This gives you an audible alarm, using the sundial, but it also works during the night.

The lens effect could also be used to maybe melt wax used to plug the hole in Pablo Oliva's Clepsydra too. Sure, it's an extra step, but it could work.

Edited to address some stuff brought up in the comments. Thanks guys!

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    $\begingroup$ This is genius. $\endgroup$ – Erin Thursby Nov 13 '17 at 21:39
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    $\begingroup$ I like the idea. However, as explained here, what-if.xkcd.com/145, light from the moon can't be used to start a fire. $\endgroup$ – Billy S Nov 13 '17 at 22:02
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    $\begingroup$ Just the Candle Clock is worth an upvote. If you can standardize a candle to burn predictably you can light it yourself at a given time and side step lens jiggery-pokery. $\endgroup$ – Willk Nov 13 '17 at 22:21
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    $\begingroup$ Cool idea. Not gonna work. You will need several days to align your lens and candle (with still a fair chance to miss). And then a tiniest cloud may screw you up. But even if not - why bother at all with that set-up if it is activated during the day, so you could just light it up yourself? $\endgroup$ – Headcrab Nov 14 '17 at 0:36
  • $\begingroup$ Agree with @Will, a bigger candle clock would eliminate the faffery of how to light it. $\endgroup$ – Nuclear Wang Nov 14 '17 at 13:53
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In the TV show Rough Science S02E03 they built a super accurate sun clock. But then they wanted to chime the hours, so they made a water clock and calibrated it against the sun-shadow clock.

Narrator: Mid-afternoon, and the quest for the perfect bong rolls on…
with coconuts.     {13 minute mark}

Any number of physical proceses occur at a pretty steady repeatable rate. They might not be good for long-term accuracy and may require resetting the apparatus frequently so they are not primary clocks that simply and reliably give the time of day. But they are still available for specific purposes, and not hard to invent.

He should be able to obtain hourglasses, time candles, etc. without any special novelty.

The jerry rigging is to arrange for an automatic alarm from such items. Candles are more practical than sand for an 8 hour span — time candles will be marked in quarter hour intervals and last 8–10 hours. Tie a string around the candle at the proper mark. When the string is released, it lets loose a bucket of water over your bed, or somesuch.

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    $\begingroup$ I love the Rube Goldberg vibe on this one. $\endgroup$ – Paul TIKI Nov 15 '17 at 0:16
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Light is really good at waking people up. It doesn't take a very bright light to rouse someone. If you are not habituated to an alarm clock, then the first light of dawn is usually sufficient to awaken you.

Light can awaken one far earlier than their normal time to get up. I awaken at dawn, but if someone in my house leaves the hall light on at midnight, the light coming under my bedroom door is enough to make me stir and open an eye to see if it's time to get up.

So, use the moon. Use lenses to focus the moon's light, when the moon is in the right position, on the person's face.

If the person sleeps on their stomach, give them a night shirt with something uncomfortable on the front (stones, studs, etc.) to keep them from rolling over onto their stomach.

The sleeper should avoid strong drink or anything else that might interfere with their natural tendency to awaken when it is light.

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    $\begingroup$ The moons size, appearance and location in the sky varies dramatically in a short period of time, you can't rely on moonlight to do this for you. $\endgroup$ – Binary Worrier Nov 14 '17 at 7:56
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    $\begingroup$ @BinaryWorrier The location and orientation of a person's head on their pillow also varies dramatically in a short period of time! Oh, and cloudy weather is a thing. So, really, this is a total non-starter. $\endgroup$ – David Richerby Nov 14 '17 at 16:07
  • $\begingroup$ @BinaryWorrier The spec, as I understand it, is to awaken a person at one time on one night. The lenses are aligned with the predicted position of the moon at that time on that night. $\endgroup$ – Wayne Conrad Nov 16 '17 at 20:09
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    $\begingroup$ If there is a moon, at the right time, on a cloudless night, with a window facing the moon. $\endgroup$ – Binary Worrier Nov 16 '17 at 20:12
  • $\begingroup$ I admit it's not the greatest idea this site has ever seen. $\endgroup$ – Wayne Conrad Nov 16 '17 at 20:43
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Considering the level of technology, a waterwheel in a river might work, if you don't need it too exact.

The waterwheel could either fill a reservoir, which when full pours on the character, or the wheel turns enough times to tip an already filled reservoir onto the sleeper. Unless there's a drought or storm, the wheel should turn fairly constantly, given the size, weight, and radius of them.

This could lead to problems arising from the aforementioned drought and flood conditions, causing the character to get up at the wrong times, and could be part of the story. If that's not your goal or not important, then whatever. ;-)

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  • $\begingroup$ I'm not sure why you think that the flow of a river is fairly constant except for droughts and storms. The flow isn't ternary like that. There's a whole range of flow rates, and "drought" and "storm" are just the two extremes. $\endgroup$ – David Richerby Nov 15 '17 at 9:20
  • $\begingroup$ I've never paid any attention to the rivers I've lived near, so would the word "predictable" work better? $\endgroup$ – computercarguy Nov 15 '17 at 14:34
  • $\begingroup$ I doubt one could predict it with the necessary level of accuracy without detailed modelling and computations based on the amount of rain that's fallen upstream over the last several days, along with tidal data if you're close to the river's mouth. $\endgroup$ – David Richerby Nov 15 '17 at 15:06
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I second clepsydra, but there was a real people's job in the Victorian era to walk around the houses and knock at the windows with a long stick to wake up people.

In the more industrial era, the workers were woken up by the steam whistle of their factory, as they would typically live nearby. If there is some kind of industrial activity around your hero's sleeping place (like a forgery, it can by long predate the actual industrial revolution) he might wake up by the noises from it.

Or is there a leather tanning nearby? Let the window open and be waked up by the smell, esp. if the wind in the morning is in a (non-)favorable direction, as opposed to evening.

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    $\begingroup$ This could be vaguely associated with the window-clock by leaving something in your window that corresponds to the time that you want to be woken. $\endgroup$ – Brent Hackers Nov 14 '17 at 11:31
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If you like the idea of using the moonlight, I would suggest using an hourglass type of arrangement. Have sand pour onto a counterweight that raises the curtains at a given time. I hope this is not too complex a mechanism.

Basically, all you have is string that goes through a pulley. One end is attached to the curtains (possibly weighted) and the other end to an empty sack. Sand falls into the sack hourglass-fashion until it is heavy enough to raise the curtain.

Not super-accurate but maybe that's not bad. The character is wakened by the light and can check immediately how much time he has to do his task. It's silent in case the castle walls are not very soundproof. Hourglasses should be a familiar technology so it shouldn't be too hard to rig up. Servants must have a way of waking up early to get things ready for the nobles so perhaps there are some of these ready to hand somewhere.

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Train a bird.

It is unclear from the OP how much time is available to develop the light triggered alarm, but given sufficient time I would have thought the best method would be to train a bird to recognise the critical pattern and then to awaken the person, maybe by pecking their head (less likely to awaken others), but there are other things that birds can be trained to do, and they can certainly make a noise if necessary. Birds are very good at pattern recognition.

https://en.wikipedia.org/wiki/Bird_vision https://www.frontiersin.org/articles/10.3389/fncir.2014.00122/full

One of the advantages of a bird is that it will make adjustments for variable light conditions, still recognising the critical combinations. This is a very simple and effective low tech solution.

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The only way I can see it working with the clock specifically is with a system of mirrors/lenses that combine all the lights from the different panes into a single focused point, at a specific time. If it was bright enough, it could focus to a point of heat. I would focus it onto a spot of some material that is especially flammable. Like a candle wick coated with something to make it ignite at a lower temperature. From there, it could either burn through a rope that is holding a small weight suspended over him, or the heat could turn a small chime (something like this: https://www.amazon.com/Biedermann-and-Sons-Inc-H-350/dp/B000VUX5VK). It's a stretch - the water clock ideas are much more realistic - but it could theoretically work.

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    $\begingroup$ That won’t work with moonlight. $\endgroup$ – JDługosz Nov 13 '17 at 22:29
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    $\begingroup$ I would suggest a different post on the same subject $\endgroup$ – Luke Nov 13 '17 at 22:48
  • $\begingroup$ I noticed this answer after posting mine. I deleted mine and want more people to look at this one, because it's the right solution. It just needs a bit of tweaking. Ignore the existing sun dial clocks completely. Use enough mirrors to capture the moon light, use prisms to direct the light over a gap between stones. The angle of the prism, placement of the stones, and width of the gap dictate when and for how long the "alarm" takes place. A mirror at the bottom of the gap directs light to focusing lenses. Use a band of bright light rather than a dot. Not bright enough? Add more mirrors. $\endgroup$ – JBH Nov 14 '17 at 1:20
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    $\begingroup$ Bear in mind, we're not trying to start a fire (oddly, despite the links provided, I've started a fire by moonlight using a magnifying glass....), we're trying to wake someone up. All that means is bright, not hot. (BTW, The salient quote from @Luke's link is "That's too cold to set most things on fire." It depends on what you're using for tinder.) $\endgroup$ – JBH Nov 14 '17 at 1:27
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    $\begingroup$ @JBH I suppose the important phrase is: The Moon's sunlit surface is a little over 100°C, so you can't focus moonlight to make something hotter than about 100°C. That's too cold to set most things on fire. (emphasis mine) $\endgroup$ – Baldrickk Nov 15 '17 at 13:05
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Since a "sun" dial requires light to function, I will like others, assume moon light will indicate time accurately on this night. Place a mirror a the appropriate hour on the dial. Use several to focus the light to increase the lumen of Luna. Direct this light to a crystal or glass sphere that illuminates the area where the hero is to the point of waking him.

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  • $\begingroup$ Focusing makes the spot smaller, and illuminating the area spreads it out. So that doesn’t make sence. What you mean is just to allow moonlight into the room onlyafter the desired time, which is a sound idea but won’t involve lenses. $\endgroup$ – JDługosz Nov 15 '17 at 21:48
  • $\begingroup$ @JDługosz True. But the focusing is intended to concentrate the light to a specific area (the orb) at a distance (across the room by the bed). The net result is the same, but the bed doesn't have to be near the "moon dial". $\endgroup$ – Jammin4CO Nov 15 '17 at 22:32
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A candle Clock:

https://www.pyramidtimesystems.com/Blog/BlogView.asp?BlogId=4096820&CategoryID=10

A pin set into the candle at a specified height falls when the candle burns down, making a loud clanking and waking someone.

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    $\begingroup$ And put another one some way down the candle for a snooze button. :) $\endgroup$ – DonielF Nov 14 '17 at 23:56
  • $\begingroup$ Post the actual URL please, not the Google result link. $\endgroup$ – JDługosz Nov 15 '17 at 21:53
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@LeeLeon was close but I think this merits an answer rather than just a comment.

  • Take a bird that sings at dawn -- perhaps a cockerel, perhaps something more pleasant-sounding.
  • Place it in a darkened cage (make it out of metal so the inside is shiny in case the bird faces the wrong way; the metal will block ambient light), with a window (or even a lens) on one side.
  • Align that window to face where the moon is due to be at the appropriate time (probably placed on the window-ledge of the room)

    • This is near enough the same as the previous night
    • Also it can be predicted from tables by someone with the skills of a ship's navigator
    • In fact such predictions are built into the clock system described in the question.
  • When the moon shines into the cage, the bird wakes up and starts singing, waking the sleeper.

This could be set up with little preparation, especially if the character is in a position to have a cockerel (farmer) or cagebird (anyone with time/money for frivolities or affectations).

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You can't use the moon for a sundial because there isn't a moon in the sky every night also the rise and set times of the moon changes.

To use the moon, the moon can't orbit the planet. It would need to appear and disappear like clockwork.

Said "moon' would need to be a planet with the same orbital rotational speed as the planet. Perhaps a gas giant reflecting the sun's light?

Candles, if made the same, burn at the same rate and could be turned into a crude alarm clock in a pinch should other none sundial clocks be available.

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    $\begingroup$ The only way you can have two planets with the same orbital period is if they're in the same orbit. And even that wouldn't work because they'd obviously have to be in different positions in the orbit. Orbital speed isn't constant (orbits are elliptical and the planet moves faster when closer to the sun) so two planets in the same orbit will be closer or farther apart at different times of the year. $\endgroup$ – David Richerby Nov 15 '17 at 9:27
  • $\begingroup$ Exactly. You can't use a moon for a sundial type clock. $\endgroup$ – Thorne Nov 16 '17 at 2:46
  • $\begingroup$ My point is that you can't use a planet, either, which is what your answer proposes. $\endgroup$ – David Richerby Nov 16 '17 at 8:29
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How about using a combination of mirrors/prisms/lenses to shine the hero in the face at a particular time?

Since your world uses different color combinations of light to show time, we might also be able to use these color frequencies to reflect towards the hero's sleeping area.

Then again I have no idea how this would work (makes hand wave gestures). And of course when the light is disrupted or the hero is not at the spot where we would aim our reflected lightbeam this would have no chance of working either.

Either way. This adds up to something that your world would be able to use, but you will need to find your own scientific explanation.

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  • $\begingroup$ The problem with anything based on the moon is that the moon's behaviour is extremely variable. First, the phases mean that you'll get almost no light for one week out of every four (which happens to be this week). Second, the moon rises and sets at completely different times each day -- at the moment, where I am, the moon is rising each day about an hour later than it did the previous day and in a week or so, it'll be rising later than 10am. Third, not only is the new moon in a few days' time but also, it's going to be cloudy tonight. You're not gonna be woken by the moon tomorrow. $\endgroup$ – David Richerby Nov 15 '17 at 15:12
  • $\begingroup$ @DavidRicherby The OP never states the situation to be ON the moon, just by night. He also claims dials work at night, just not as much. Which should not be a problem. You are right about some inconvenience setting and adjusting the alarmclock each day to adjust with the moon's orbit. But the OP never claims it works the same way as our earth-sun-moon system. $\endgroup$ – Totumus Maximus Nov 15 '17 at 15:44
  • $\begingroup$ By "based on the moon", I mean "derived from the moon" not "physically located on the moon". As in, "The movie Romeo + Juliet was based on Shakespeare's play." $\endgroup$ – David Richerby Nov 16 '17 at 8:32
  • $\begingroup$ @DavidRicherby ok i misunderstood. Sorry $\endgroup$ – Totumus Maximus Nov 16 '17 at 8:55
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Magnifying glass add-on for the ligth emiting thing , pointed at somthing that might breack or do a buterfly effect and hit the lead in order to wake him/her up.

Or what the comments already said about drinking extra water

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There are several time pieces that are in side your tech range that would work just as well.

A simple design would be a "water clock" that just overflows onto ones bedding.

Greeks used a kind of "hour glass" that made a sound when all the water or pebbles got to the bottom jug.

Native Americans used lots of water at certain times before bed to make sure they woke up on time in the morning.

Many animals can be used (think rooster) depending on when you need to get up. A hungry nocturnal predator in your bed room will surely wake you up.

Chinese and Arab inventors had "striking clocks" as early as AD 650ish.

Depending on how rich your people are, it would not be unreasonable for them to have a clock, with an alarm.

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    $\begingroup$ And, er, how do you propose to arrange for a hungry predator to enter the room at the right time? $\endgroup$ – David Richerby Nov 15 '17 at 9:49
  • $\begingroup$ You don't. You just let it sit there. When it starts hooting or chewing on you, it's time to wake up. Anyone with dogs has to go through this phase. $\endgroup$ – coteyr Nov 15 '17 at 12:24
  • $\begingroup$ OK. So how do I arrange for it to start hooting or chewing on me at the time that I want to wake up, rather than the time that it wants to hoot or chew? If I'm happy to wake at any random time, I don't need to do anything; the question is about waking at some specific time. $\endgroup$ – David Richerby Nov 15 '17 at 12:36
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    $\begingroup$ You choose an animal that reacts near your time, or train it. For examples farmers waking up to roosters. Guess it depends on how accurate you want to be, but animals can be surprisingly accurate. $\endgroup$ – coteyr Nov 15 '17 at 15:28
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    $\begingroup$ @DavidRicherby Ha, that could be a business! Stop at the livery on the way home, “I'd like to rent a 4AM dog, please.” They train animals to expect breakfast at various times and keep a supply. $\endgroup$ – JDługosz Nov 15 '17 at 21:52

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