Monitor's magnetic field setting off handheld CO detector

[flatmosquito]

TL;DR Summary

monitor's magnetic field setting off handheld CO detector

Hi, I have a small handheld CO detector (https://www.amazon.com/gp/product/B08SQPKTGN/?tag=pfamazon01-20), and I've noticed that leaving it on my desk near my monitor will invariably trigger the alarm. There are magnets that are housed at the base of the monitor (an old mac Thunderbolt display) that I can confirm by sticking various steel items to.

I know the CO detector can work via "electrochemical sensors, metal oxide semiconductors or biomimetic sensors," but I don't know which one this detector uses. And I also have no idea how a magnetic field might trigger the alarm - is anyone familiar enough with the electronics that might be housed in here to give me a place to start understanding this?

Thanks!

 

[berkeman]

Welcome to PF.

Does it seem like it's the DC magnets that are causing the false alarms, or is it something in the body of the flat panel display (like the power supply)?

Does the label on the back of the unit have a "CE" logo on it? That would imply that it's been tested to European immunity standards, so should not be overly sensitive to external interference sources.

But even with a CE mark, strong DC magnetic fields can saturate inductors in the device, which could do all sorts of bad things. The good news is that those inductors generally use "soft" ferrite cores, so there will be no residual magnetic offsets in the inductors after you move the device away from the DC magnetic field.

Does the device seem to work well in all other settings?

(Also, are you a firefighter? Is that why you have a CO detector in your kit? Asking for an EMS friend...)

 

[Dullard]

There are a couple of reasonable possibilities - neither of which involves the magnets:
1. The kind of sensor typically used in a hand-held battery-operated CO sensor is a high-impedance device. There will be signal conditioning/processing hardware, but the fundamental sensor is susceptible to 'electrical noise - particularly in the 'upstream' part of the circuit. The plastic case for your device probably does little to help - the manufacturer would (if you spoke Chinese) probably tell you not to use it near powered devices.

2. This kind of sensor typically has 'cross-sensitivities' - it responds to more than just the species of interest. This seems less likely than #1 (in your case), but it is a common issue with 'budget' sensors.

An experiment: Unplug the monitor (and the associated computer). Rule out/in #1.

 

[flatmosquito]

I think there is something to the power supply possibility. Today I noticed that just putting my cell phone next to the CO detector will set it off - and it even gave a 200 PPM warning when it's been reading 0 PPM for days.
I have the CO detector because I had actual CO issues in my apartment last year, as verified by the fire department, so I bought some of my own detectors. But this one is possibly too cheap to really be relied on...

 

[berkeman]

Yeah, there is no way that a cell phone next to it should set it off. Glad you are okay after the CO incident at your home -- those can be insidious.

 

[Rive]

But this one is possibly too cheap to really be relied on...

A rugged one would cost a fortune. I would certainly test it (the one we got was some fire-department recommended type from a proper store, but even so, I still tested it) for sensing CO, but if the only problem it has is just being allergic to monitors and mobile phones, then it's just matter of attention I think.

 

[Dullard]

I agree with Rive. I would add:
Precision is cheap - accuracy is expensive. This thing is probably OK as a gross detector. If it shows 'some' CO, I wouldn't assume that the number on the display is particularly close to the actual concentration.