ESP32 Freezer Alarm Keeps Tabs On Tricky Door

Leaving your freezer door open accidentally is a great way to make a huge mess in the kitchen. [Guy Dupont] had a freezer that would regularly fail to close properly, and was sick of the regular meltdown events. Thus, he whipped up a very digital solution.

The build combines an ESP32 with a reed switch, which is activated by a magnet on the freezer door. If the freezer door is open, the reed switch similarly remains open. The ESP32 checks the switch status every few minutes, and if the door remains open for two consecutive checks, it raises the alarm. A notification is sent to [Guy] via WiFi so that he can rectify the situation. The rig runs off a 400 mAh battery, which lasts for just over three weeks running door checks at two minute  intervals.

Based on [Guy]’s YouTube video, it appears the freezer door is jamming up against the wall. Perhaps shoving the freezer into a better position would help, though we suspect he would have thought of that first. And, in his own words, “That would be a very boring YouTube video, wouldn’t it?”

It’s not the first fridge alarm we’ve featured, and it won’t be the last, refrigeration gods willing.

31 thoughts on “ESP32 Freezer Alarm Keeps Tabs On Tricky Door

  1. Why not use the reed switch to bias a FET off when it is closed, and power up the ESP32 to time out after tow minutes and then send an alarm? That battery should last almost forever thatr way?

    1. Original dev here. This would indeed be better. I think I was working on deep sleep stuff for something else and just had it on the brain at the time. I think I may have also been better off just using the pin to wake from sleep but I vaguely recall seeing that that would draw more current?

      1. I remeber that the esp8266 had about 20uA of deep sleep and you can go as low as 3uA with some hardware mod (i belive a pulldown resistor was to blame for the high current consumption). But the esp32 should have a better hibernation/sleep

  2. A wood shim between the wall and fridge would have been easier/cheaper solution, but I like that he made something. 🤗

    And it makes for a reason to make a video..

    1. /me tilted the freezer ever so slightly that the doors fall shut by themselves. Takes some time to get used to (WAF is so in the middle) but works without anything else.

      A beeper was not in the budget, so it seems. Would have preferred that, too.

      1. Are there upright freezers that don’t have levelers on the bottom?

        (My 12 year old refrigerator/freezer makes annoying sounds to let you know that either the fridge door(s) the freezer drawer have been “unclosed” for too long.

      2. I tried adjusting the legs on my freezer to do exactly that, but couldn’t get it right. So I threw a couple of reasonably strong magnets with threads on them and added some short screws so I could wrap a rubber band between the magnets. After some strategic fiddling, the door now closes itself. Or stays open if I open it wide enough.

  3. We had the problem that the door would bounce open when we closed it so now our fridge/freezer tilts back around 3° so it never stays open because of the bouncing. (Things might still prop it open.)
    Since this is hackaday: A 555/556 could be used if you only need audio cue.

    1. A RasPi, communicating to another remote RasPi, which communicates to IFTT, running a “lighweight MQTT” framework, you know, something that a lowly i7 with only 16gb of memory could run, which when it receives the message, sends output to alexa, which sends an MQTT to IFTT, blah blah…

  4. Not a great design IMHO.
    ESP32 already has a built-in Hall Effect sensor, use it not the reed switch
    It should also have a temperature sensor to alert if the freezer temp goes up. ESP32-S2 has one built-in.
    Condensation will be a problem, it needs a box or conformal coating.
    How does the WiFi signal make it out the metal box, the door may not be open by that much.
    Li-ion pouch batteries minimum is -20°C discharge and their impedance goes up quite a bit when that cold – not enough for an ESP32 WiFi TX packet at 500mA burst.

    My Whirlpool fridge the freezer door did not close all the way and it kept running and iced up the evaporator.
    What a hassle thawing that out. So there is a need for this but I would go old school 8-bit MCU lol.

    1. > How does the WiFi signal make it out the metal box

      I’m not sure – you would think it was a Faraday cage, but it does indeed get out. I recently had a suspicion that my fridge’s thermostat wasn’t doing its stuff. So I knocked up an ESP8266/BMP180 circuit and logged the temperature on the ESP. I was however able to access a web server on it from outside the fridge.

  5. Good video, and honest.
    My suggestion is, since this is a “real” ESP32 (not a -s2 -s3 version), you could use the built-in Hall effect sensor on the ESP32 with the magnet and avoid the reed switch.

  6. Always love there is a better way to do almost anything.
    That’s hackday for you, come up with a great solution and unless you hit gold, always someone has a twerk or alternative. It’s how we all learn.

    OH! If it was your day to get the golden solution, maybe you should have bought a lotto ticket, well with luck like that😎😎🙏

  7. It would be much better to use temperature to monitor the freezer door. In this way, if you power the unit with a battery, you also get an alarm if the power fails, or if the freezer fails. The unit should be fitted outside with the temperature sensor fitted through a sealed hole. It can then be powered by a charger normally and only use the battery when the power to the freezer has failed.

  8. I have one of those cheap 433MHz thermometers inside my freezer door. It powers from three AAA cells which last over a year. When the temperature increases over a threshold, the door isn’t properly shut and i get an alarm via pushover on my iphone. Apart from that it’s also interesting watching the triangle shaped cooling/heating-up waveforms

  9. I had the same problem with a refrigerator and freezer in my pantry. Kid/Spouse would not check the door, and I would end up with thaw etc. It also affects the lifespan of the newer appliances since they build the chilling systems with such tight margins.

    My not yet completed (though many times tested and demonstrated) system measured chamber temps to determine if there were problems. It also allowed me to track efficiency and know when a refrigerator or freezer was about to die (my spouse would always say “I thought it felt warmer, I was going to say something”).

    Latest generation will give a voice alert and allow for a button press to give current temperature readings. ESP8266 and audio board to pull that off.

    Ties into the home automation Pi for logging and e-mail/text alerts. Also hosts webpage for checking.

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