Introduction: Extremely Loud Low Filament Alarm - Version 1.0

About: Welcome to my Instructables channel where I'll share my wacky and unique creations that hopefully others find useful, or better yet, inspire an evolution of even better ideas!

UPDATE 02 AUGUST 2020: With the help of fellow users, I was able to create a better, cheaper, and easier to make version. Please see Version 2.0.

A simple, cheap ($16), and LOUD, low filament alarm for bottom up filament feed direction 3D printers.

This is an entry in the Rainbow Contest. Please vote if you like it. Thanks!

PROJECT SUMMARY: This alarm attaches to a FDM 3D printer's filament line. If the filament runs out during a print, the alarm will go off alerting the user to pause the print and add more filament before the print is ruined and has to be restarted.

UPDATE 30 JULY 2020: There have been some really good comments from other users, and Daboke had a great contribution. The comment was, "Why not use just the Window Alarm? Which was truly one of those "Why didn't I think of that?" moments. I was so focused on using the Dump Switch that I was completely blinded to a much easier solution. I'm working on that concept now, and will most likely post it as a separate Instructable. Thanks Daboke.

NOTE: Ignore my Side Stories if you want to get straight to the build.

SIDE STORY: This was supposed to be part two from this Instructable. However, I gave up on trying to find a digital scale that stays on all the time to continuously monitor my filament use. The idea was to simply place my filament bobbin holder (Instructable Link) on the scale with an empty bobbin, tare the scale, then load a full bobbin filament. The scale would then give you a real time readout of just your filament (so a new filament will start at 1000 grams). Each time you generate a Gcode file (I use Cura), it will tell you how much filament that particular print in both grams and meters will require. So, if you're close to the end of your reel, you can check the scale reading to make sure you have enough. But, I think this alarm is better, since you don't have to do anything once its loaded.


  1. Window/Door Security Alarm
  2. Dump Switch
  3. M4 Screws
  4. Small gage (20AWG) wire
  5. Terminal Plug, Solder Style
  6. Solder/Flux/Heat Shrink Tubing


  1. Soldering Iron
  2. Heat Gun
  3. 3D Printer

Step 1: Dump Switch

The key component to this design is called a dump switch. Its used in a variety of products, but the most common is in consumer electric heaters. If the heater is tipped or falls over this switch activates and cuts power to the heater for safety.

In this application I need it to turn ON when it tips over not OFF like its intended function. To do this, you have to tap into the switch by attaching a wire to its normally open (NO) lead. And since we won't be using the normally closed (NC) lead gently bend it back and forth a few times to break it off. (See image above with the NO and NC leads marked.)

SIDE STORY: I purposely did not do any kind of internet search to see what filament alarms are out there before starting this project, because I wanted to see if I could make this idea work without any outside influence. After I finished this, I did do a search, and was pleasantly surprised that while there are a ton of designs out there, I didn't see anything that uses this type of switch. And also, the ones I did see were not very loud.

This thing will wake up everybody in the house if it were to go off during an overnight print!!

Step 2: Window/Door Alarm

The alarm just needs a few tweaks for this application.

  1. Toss the magnet. It is not needed.
  2. We need to break the alarm's power (4 small coin batteries) connection and wire that into the dump switch. So, when the filament runs out and the alarm falls over, the dump switch activates and turns power onto the alarm, and since the magnetic component of the alarm is missing, it will sound the alarm as soon as it gets power.

Initially I was going to make the connection on the motherboard, but it was too small and would have needed more work to route the wires, so I simply used the batteries as the switch. A single layer of double-sided tape between the two center batteries with one wire on each side works perfectly (Second image above - Click it to see the full image). Only had to slightly open up the housing to feed the wires through while still allowing the battery cover to still slide into place.

TIP: Don't select "CHIME". Select "ALARM". (If alarmed in chime setting, it only chimes once then stops. If alarmed in alarm setting, it sounds the alarm continuously.)

Step 3: 3D Print the Alarm Housing & Lid

This was designed in Fusion 360, sliced in Cura, and printed on Ender 5.

Step 4: Gather Parts & Assemble

Assemble as shown in the images above, using the M4 screws.

NOTE: The threads are modeled in the .stl files, so no need for inserts or tapping.

Step 5: Finished

As you can see in the images above, the large "V" shape on the bottom of the housing notches into the 2040 rail.

Another benefit of this design over what I saw others doing is this can be attached to filament that is already inserted in the printer. The three alternating clips are sized such that you route and clip the filament in.

NOTE1: It may look like it will balance in place (and therefore not work), but I designed it so the center of gravity (CG) is off center. (It wants to fall to the right in the images above.)

NOTE2: When doing a filament change, remember to turn the alarm off BEFORE removing the filament or you will scare yourself badly and feel dumb afterwards. Not that I would have done that, just warning others. ;)

Thanks for taking the time to read through my Instructable. Please send me any questions or comments you might have. I try to answer them all. Stay safe and healthy! Happy Printing!

Colors of the Rainbow Contest

Runner Up in the
Colors of the Rainbow Contest