Stove Alarm Keeps The Kitchen Safe

Gas cooktops have several benefits, being able to deliver heat near-instantly, while also being highly responsive when changing temperature. However, there are risks involved with both open flames and the potential of leaving the gas on with the burner unlit. After a couple of close calls, [Bob] developed a simple solution to this safety issue.

The round PCB sits neatly behind the knobs, affixed with double-sided tape.

Most commercial products in this space work by detecting the heat from the cooktop, however this does not help in the case of an unlit burner being left on. [Bob]’s solution was to develop a small round PCB that sits behind the oven knobs. Magnets are placed on the knobs, which hold a reed switch open when the knob is in the off position. When the knob is turned on, the reed switch closes, powering a small microcontroller which beeps at regular intervals to indicate the burner is on.

It’s a tidy solution to a common problem, which could help many people – especially the elderly or the forgetful. It integrates neatly into existing cooktops without requiring major modification, and [Bob] has made the plans available if you wish to roll your own.

On the other end of the scale, you might want an alarm on your freezer, too.

70 thoughts on “Stove Alarm Keeps The Kitchen Safe

  1. I love this! I have an electric stovetop, and I’m incredibly forgetful. I’ve ruined numerous pans by leaving them to boil, they boil dry, they warp…

    In the interim, I’ve just been super rigorous about setting timers when I walk out of the room. But long-term, I’d like a motion-sensor that simply kills power to the stovetop if I haven’t been in the room recently. Optionally beeps before doing so, so I can trot back in and check on things.

  2. “Magnets are placed on the knobs, which hold a reed switch open when the knob is in the off position.”
    thats according to hackaday, btw and FYI the magnet does not hold the reedswitch open, there is just no magnet in the vicinity of the reed switch when the circuit is open, that said the idea is good but does that mean it beeps all the time even when he cooks?

    1. The magnet absolutely does hold the reed switch open.

      From the link:
      “The burner knob has a small magnet stuck to it, and when the burner is off, the magnet is positioned over a Normally Closed reed switch.”

      This is also known as a “reverse reed switch”. This way there’s no power when off, but power when in any position *other* than off without needing a whole ring of magnets. And yes, it beeps while he cooks at the increasing intervals specified in the writeup.

        1. After the first 10 minutes, it beeps three times. After the next ten, it beeps 6 times. Then 9 times, and so on. I have found that it is not annoying. If you’re going to have something on the stove for a long time and it’s really bugging you, you can turn the burner off then on again, which will reset the counter.

    1. No power flows when the burner is off, and the microcontroller sleeps in between beeps. I expect the battery will last a long time.

      When the burner is first turned on, it beeps once. If you don’t hear that, you know the battery is dead.

  3. The only advantage of a gas cooktop I can think of is low TCO. As far as control is concerned electric (especially induction) ones are by far more convenient. Mine has a timer (separate for each field), it detects if a pot is present (induction) and enables very accurate control at the low-power end which I have never met in a gas powered one. And there is now risk of blowing anything off since I’ve got no gas at all.

    1. The advantage of gas is high heat output for houses with small electrical connections. A typical connection for an electric range has 220 Volts and 40 Amps, which gives 8800 Watts, which is divided between the oven and four hot plates which may all be on at the same time. Usually the big hot plates, induction or otherwise, won’t put out more than 2000 Watts, though they might come up to 3700 W.

      Meanwhile, gas stove burners typically max out at 18,000 BTUs (5300 W) and even if half the heat goes up the flue, that’s still more powerful than the common electric range.

      1. And, try using a proper round-bottom wok pan on an electric stove.

        Can’t be done. Using a flat-bottom wok on an electric hot plate is just fooling yourself, because it just doesn’t get hot enough and it doesn’t work like a wok – it’s just a funny shaped pan.

          1. Wok pans are made of carbon steel and they’re seasoned by bringing them to a dull red heat, then swirling a little bit of oil in it, which polymerizes on the surface and forms a non-stick coating. It’s kinda like how you’d season a cast iron pan, but much hotter.

            This doesn’t work on induction stoves anyhow, because getting the metal to red heat changes its magnetic properties and the stove thinks it’s not there anymore.

      2. The open flame on a gas burner also allows you to roughly gauge the temperature of the burner. I find it easier to remember what flame size to use in staid of what number on a knob.

        1. I try to use more accurate feedback loop and observe what is happening in a pot. When I am cooking something I keep turning the power down until it stops boiling all the time (it boils for a few seconds and then stops and again). With an induction cooktop having very little inertia it appears to be very accurate. On gas cooktops I have used, I can’t set the flame that little. And I have yet to see a gas cooktop with timer controlled valves. I love timers.

          1. That works for liquids, but not all foods have such a convenient feedback mechanism. When I make a grilled cheese sandwich, for example, I found that if I set the flame slightly past where it starts to curl over the burner, and flip the sandwich just after it stops sizzling, the sandwich turns out good. To much or to little heat and the bottom of the bread burns and the rest is still raw. You do make a good point about the timers.

          2. On gas stoves, you put the food on the smaller burner. The lowest they’ll go is about 1000 BTU (300 W) with the bigger ones, and 400 BTU (120 W) on the little ones. If you need less heat than that, two tea candles make about 80 Watts.

            Electrics usually have six power settings, 2000 W, 1500 W, 1000 W, 500 W, 250 W, 125 W with the first setting just meant for keeping the food warm.

          3. @Luke
            How about efficiency? I suppose there is little chance that a pot can get more heat from hot air flowing around it that from electric current induced inside its walls. Even resistive heater should deliver more heat than hot air per watt of input.

      3. Yes, if the connection is a problem then gas is a way to go. You wrote about 220V at 40 A, which made me wonder what kind of a connection is that? I assume this is in the USA. In Europe the usual connection is 3*230V at 25 A which is 17kW. More than enough for four plates, an oven and to keep your lights from getting dim.

        1. Split phase 220 Volts is common in North America. The appliances run on the full 220 – 240 V output while the sockets are using the center tap from the transformer.

          The cooktop has its own breakers, commonly 40 Amps, while the whole house has typically 100 – 200 Amp breakers at the panel. The washer/dryer gets another 30 Amps, the water heater another 30 Amps, and that’s about it. If you have 100 Amp service and you put everything on at the same time, you may pop the breakers. Of course these devices don’t pull the full amount to leave a safety margin, and the water heater or dryer may also use gas, which then requires a smaller electrical connection.

          Old homes may go as low as 60 Amps, but breaker panels this small aren’t being installed anymore. Small apartments and studios can have anything – usually not very much.

          1. I was visiting relatives back in the old country for Christmas. They had 3×50 Amps service. Zero degrees outside, oven on, hot plates on, ventilation on, all the lights on, TVs, stereos, fridge, chest freezer… water heater turns on… and half the house turns off.

            That’s one of the problems with multi-phase distribution. You can’t really distribute the loads very evenly, whereas with single phases to each house, all the amps are available to all the devices.

            It’s even better for the grid, because you can balance the load between the phases at the distribution transformer instead of inside the house. Using an open delta transformer to pull 3-to-1 phase, the load distribution on the three phases is 1:2:1 and for each house along the line you simply rotate which phase has the biggest load. There’s different connections for different load distributions, so you can mess around with it at the pole, giving more freedom for pulling their house wiring for the homeowners.

          2. @Luke
            What if you go for holiday and your neighbour starts an overhaul in his house? It doesn’t look like an even distribution, does it? And I am sure electric company guys doesn’t appear more than once or twice a year for maintenance in a neighbourhood, if they don’t really need to.

        2. Yes some of us USA folks envy your 3-phase power in home. It’s split-single-phase 240/120V power here… my electric range & oven is on a 50A circuit (using a NEMA 10-50 plug, though newer homes use a 14-50 with separated ground & neutral line).

          1. The low voltages are only after the distribution transformer, which is often much closer to the home.

            The voltage up to the transformer is between 2.3 – 11 kV, usually 4 kV depending on the local grid. The last few hundred feet are 240 Volts, which is practically identical with the European three-phase power where the loads are connected between phase and neutral – which is usually the case for regular household appliances.

            Even for the big appliances like washer-dryers in the EU, they almost always plug into a single phase instead of using all three. The water heater is in one phase, the washer in another, the stove -may- be three phase but might just as well be single phase. Lights are in one phase, sockets in the other, or one room’s sockets may be in a different phase than the other’s… etc. which sometimes creates interesting effects in audio and network cables from one room to the next.

            So, for all the regular appliances you might find in the house, the NA system doesn’t differ in efficiency from the EU version, and for all the smaller loads like lightbulbs and sockets, it offers a safer voltage.

    2. Fast response, is what a chef will tell you.

      The time lag of an electric element makes them frustrating to cook on. I’m certainly no chef, but on my electric, I’ve learned to anticipate where I want the heat to be for the next minute, and dial it in ahead of time. If things get too hot, I’ll scoot the pan over to a cold burner rather than turning down the knob, because the latter would simply take too long to reduce the actual energy delivered to the food.

      Gas also works well on cookware with rounded bottoms like a wok, that don’t make good contact with electric elements or induction coils.

      We’re mostly talking about cooktops here, but I’ll mention one other important difference for ovens: Humidity. Gas ovens produce water vapor as a combustion byproduct, so the oven chamber tends to be a bit moist. Electric ovens are perfectly dry, and it’s helpful with certain foods, to place a pan of water on the bottom rack simply to contribute some moisture during baking. On the other hand, desiccant bake-out is only practical in an electric oven…

      1. Can confirm. As a professional cook who has lived and worked in many residents with eletric (not induction) ranges, I’ve learned to cook on electric by either never using every burner, or designating a safe space on the counter to move overly hot pans. Never an issue on gas.
        Though I will say I find very few times when a gas oven is the better choice over an electric convection oven with an adjustable fan.

      2. The time lag of an electric element makes them frustrating to cook on.

        It’s not an issue on induction cooktops. The only inertia there is the one of a pot which makes no difference compared to gas. I dare to claim that (without any scientific proof) that induction cooktops have better dynamics that gas ones.

        We’re mostly talking about cooktops here, but I’ll mention one other important difference for ovens: Humidity. Gas ovens produce water vapor as a combustion byproduct, so the oven chamber tends to be a bit moist. Electric ovens are perfectly dry,[…]

        Not exactly true. Unlike gas ovens electric ones need not to be ventilated. There are no combustion products to be removed to make room for fresh oxygen. And the whole kitchen needs better ventilation too. First few times I opened my new electric oven I was completely unprepared to meet the cloud of hot water vapor that came out of the oven. I was lucky I was wearing my glasses. I never had such surprises with gas ovens.

    3. “As far as control is concerned electric (especially induction) ones are by far more convenient.”

      You can’t really compare a traditional electic stove to an induction stove. No traditional electic stove I’ve ever encountered has any saftey features such as pan detection. They also cycle power on and off to maintain average heat, which leads to uneven simmer/boils at best, and unsafe canning practices at worst.

      1. Indeed pot detection isn’t available on traditional ones with heating element. Traditional power output control is also not very accurate, however, with electricity it can be done not worse than on an induction stove. My induction stove also power cycles when set below 4-5/10. Which doesn’t bother me, because it still keep the temperature above 90°C and I’ve learnt water does not need to boil all the time to prepare most stuff I do. And it saves some energy.

      2. I’ve never seen a regular resistance heater stove plate that does the on/off thing. They all have multiple heater wires inside the plate, and the switch only selects a combination of them for more or less power.

  4. My gas stove has no indicators for the oven either, not to mention the burners. Its a base model and the oven temp knob is the only indicator that its on. I think i’ll do something similar but with a blinking LED. The sound would be irritating while cooking to me

  5. I religiously set timers or stand right there. Also the smell of the additive in propane really drives me nuts so I notice it quickly. I can smell it on my hands for at least 10 minutes after I switch tanks.

  6. I would like to see a decreasing time, 20 minutes, 10, 5,5,5, at 5 start increasing the number of beeps by one.
    I never cook for just 20 minutes.
    That’s just enough time to boil water.

  7. Another beeper ugh, that’s not an alarm. I don’t wake to one. I love to jab a screwdriver into those Mallory sonoalerts.

    My oven thermostat quit, no replacement made. There is a little valve under the burners though that feeds it. I hooked up a linkage to it and jammed the thermostat open so manual control is enabled. I added a t type thermocouple and meter made for it with temperature markings to the oven. A lot of oven knob temperature is off. There never was a pilot or igniter. Start with a 1 inch high flame, wait till 400F indicated turn down to low flame and in goes the pizza. Temp is steady not on off on off. Perfect pizza moist and just the right brownness. An oven that’s as manual as stovetop cooking. Three hacks, win win win.

    What I want next to stop boiling things dry is for all four valves on the burners to have levers on the shafts behind the front and have a single motor lever them off after a selected time. They make thermostatic burners but they are pricey and subject to fail and what then. They go full heat! I will have no pressure bulb leaky controls like the oven had. It went to max when it failed! Could have started a fire! There are no safety concerns here versus the way it works normally, brain operated. Not to turn on, just off. Just like a microwave, a timed stovetop operation executed instead of another noisemaker. I killed the beeper in that too. For the forgetful it could be timed by default. This would be a wonderful safety and convenience feature on any stove.

    I wonder what oven heat and cooking messes will do to the electronics in this posted hack?

    1. The oven is elsewhere in the kitchen. The electronics are sheltered from messes by being under the knobs. It would have to be a pretty big mess to get to them.

      I know where you’re coming from about the beeps. Beeping devices drive me nuts too. But waking up to a kitchen full of gas really changes your attitude.

      The reason I had it beep three times was to make it distinctive: at least I know what’s beeping. That alone makes it a lot less annoying.

  8. A commercial product like this could have a large market of people in the very early stages of Alzheimer. Probably bought for them by friends and family. May need annoying flashing lights and also have the potential for far louder volume.

  9. We had an incident where a stove knob was bumped enough to allow gas to escape, but not enough to start the igniter. A short time later I walked into the kitchen and smelled the gas. This could have been serious if left long enough, so I decided to make sure it couldn’t happen again.

    I noticed that the knobs have to be pushed in before they can rotate. The fix was simple, a strip of fiber board just thick enough to fit behind the knobs and long enough to block all of them. When the stove is not in use, the strip is left in place. I glued a magnet on one end so it can hang on the side of the stove when we want to heat something.

      1. But they should be inherently safe.

        “This explosion, like many others, shows that the only effective way of preventing explosions and fires of gases or vapours is to prevent the formation of flammable mixtures. Sources of ignition are so numerous and the amount of energy needed for ignition is so small (0.2 MJ in this case) that we can never be sure that we have eliminated all sources of ignition. (Energy of 0.2 MJ is the amount released when a one cent coin falls 1 cm. This amount, concentrated into a spark or speck of hot metal, will ignite a mixture of hydrogen and air.)”

        While I agree unlikely, the risk is far from zero.

    1. I like the old school ones. My dad had one that had pilot lights. It still works great some 40 years later. The only reason you might plug it in was for the clock. Contrast this to the one I have now. The electronics went out, so now the oven doesn’t work at all. To use the top burners I have to light them with a match. (Yeah, I need to replace it one of these days.)

      1. pilot lights on a cook top? Of course I would repair/replace a defective igniter quickly – don’t like to get my fingers burnt by lighting the flame with a match. The oven itself is electric with convection anyway.

  10. Nice, might just do this but step it up to IOT so Alexa can play “burning down the house” at the 30 minute mark and send a message to the cell phone saying “you left the stove on” if the phone leaves the wifi area.

  11. Hardware wise it would be simpler to use a uC with an accelerometer in the knob.
    It can detect it’s own “off” position, so there is no need for any accurate positoning of the thing in the knob.

    This also opens room for much beter user interfaces.
    I very much dislike the idea of beeping every 10 minutes, Especially since when I’m cooking It takes between 15 and 25 minutes, so if this thing only starts yelling at me after the first half hour it would be much better for me.

    But with an accellerometer you can add all kind of fancy functions.
    You can build in a timer. Add one minute for each time the knob is rocked back and forth fast enough.
    This may also need a LED to keep the different timers for the knobs apart.
    You can also build in some morse code like properties.
    The inventor of this gadged also clearly never cooks soup or makes pot roas / beef stew.
    Those have to simmer for multiple hours.

    But I have an induction cooker.
    Just as fast as Gas, and as much power. Mine uses 2 phases on 230Vac. It is effectively 2 separate electrical devices mounted under the same plate.
    And only for the ease of cleaning I would never want to go back to gas.
    Cleaning is also non critical. The plate itself only gets heated by the pans on them. So there is no chance of it getting so hot untill dirt burns into the ceramics, unless you leave pans to cook dry, in which case they may heat untill the steel looses it’s magnetic properties, which is quite hot.

    Another big advantage of the induction cooker I have is the built in timer.
    I can easily set it to turn of one of the heaters of the stove after a set time.
    It also has automatic timers, which vary their time according to heat input.
    If the stove is unattended and at max heat output they turn it off after an hour or so.
    For lower power settings such a simmering the automatic cutoff increases to several hours.
    This function has never been triggered, but if I leave my stove on when I go on a multi week trip I will find some smelly rotten food on the stove instead of black charred stuff or a burned down house.

  12. Interesting detail… If you buy into the narrative that nitrous oxide from Diesel exhausts is bad for your health, you really shouldn’t use gas for cooking since gas burners will push nitrous oxide levels in the air in your kitchen far above what any Diesel car can produce.

  13. I’m looking for an alarm for oven being left on . I envisioned the alarm having like a magnetic base to place anywhere on top of the stove, and it would say to itself “I’ve been feeling this heat for 45 minutes now, so I’m sounding my alarm for someone to come cut this oven off” Once the alarm is shut off by the user as well as the oven, it would not sound again until it felt a new session of heat (despite oven still being hot). I lost count of the times I’ve left my electric oven on every time I bake.

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