# Accuracy of no touch thermometers

**URL:** <https://boards.straightdope.com/t/accuracy-of-no-touch-thermometers/939223>\
**Category:** Factual Questions\
**Created:** [April 2, 2021, 1:23pm UTC](https://boards.straightdope.com/t/accuracy-of-no-touch-thermometers/939223 "2021-04-02T13:23:01Z")\
**Posts on this page:** 20\
**Page:** 1

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**Author:** ![carnivorousplant](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/carnivorousplant/32/3563_2.png) [@carnivorousplant](https://boards.straightdope.com/u/carnivorousplant)\
**Post date:** [April 2, 2021, 1:23pm UTC](https://boards.straightdope.com/t/accuracy-of-no-touch-thermometers/939223/1 "2021-04-02T13:23:01Z")

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We record our temp when me begin work. Mine was 97.8 consistently. When the thermometer began to have erratic readings, I replaced the batteries. Now it is consistently 98.2. At the pharmacy yesterday with a different thermometer it was 97.5.  
How accurate are these thermometers, and is there a way to calibrate them?

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**Author:** ![Machine\_Elf](https://avatars.discourse-cdn.com/v4/letter/m/82dd89/32.png) [@Machine\_Elf](https://boards.straightdope.com/u/Machine_Elf)\
**Post date:** [April 2, 2021, 1:46pm UTC](https://boards.straightdope.com/t/accuracy-of-no-touch-thermometers/939223/2 "2021-04-02T13:46:19Z")

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> [@carnivorousplant](#):
>
> How accurate are these thermometers, and is there a way to calibrate them?

Supposedly pretty accurate:

> **[Are Infrared Thermometers Accurate?](https://health.clevelandclinic.org/are-infrared-thermometers-accurate)**
>
> Had your temperature checked lately with an infrared thermometer? Here’s why it’s just as safe and effective.

> [Research](https://www.ncbi.nlm.nih.gov/books/NBK263237/) has shown that, when used correctly, infrared or no-contact thermometers are just as accurate as oral or rectal thermometers.

When you say it’s “consistently at 98.2,” are you talking about readings of your own temperature? What about when you point it at other people, or at inanimate objects?

**[Here’s the manual (PDF)](https://assets.omega.com/manuals/IR200_UM-en.pdf)** for an **[Omega IR thermometer](https://www.omega.com/en-us/temperature-measurement/noncontact-temperature-measurement/human-temperature-measurement/p/OS200-Series)** that is made for measuring body temp. On page 7, it says it can measure body temp with an accuracy of plus/minus 0.5F. Assuming your thermometer has similar accuracy, then readings of 97.8 and 98.2 should be regarded as being “not meaningfully different.”

I have **[an IR thermometer](https://www.manualslib.com/manual/114639/Omega-Os540.html)** (not made for measuring body temp) with a claimed accuracy of plus/minus 3.6F in the range of body temperature, but when I measure my forehead it comes back with 89F. Hypothermia is defined as a body temp \<95F, and I feel fine, so it seems unlikely that my body temperature is in the range of 85.4-92.6F. I wonder if non-contact forehead thermometers are calculating some kind of adjustment from _actual_ forehead temperature to come up with a number that compares in a useful way with oral/rectal/subbrachial measurements.

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**Author:** ![carnivorousplant](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/carnivorousplant/32/3563_2.png) [@carnivorousplant](https://boards.straightdope.com/u/carnivorousplant)\
**Post date:** [April 2, 2021, 1:56pm UTC](https://boards.straightdope.com/t/accuracy-of-no-touch-thermometers/939223/3 "2021-04-02T13:56:09Z")

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> [@Machine\_Elf](#):
>
> When you say it’s “consistently at 98.2,” are you talking about readings of your own temperature? What about when you point it at other people, or at inanimate objects?

Taking my own temperature. I don’t have anything warm enough to point it to with a “red screen this person is dead” reading. We don’t poke things in each other’s face. I’m primarily interested in the difference in temperature after the battery change, and if I should have calibrated it. Are other people’s temperature readings the same to a atenth of a degree every day?

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**Author:** ![Machine\_Elf](https://avatars.discourse-cdn.com/v4/letter/m/82dd89/32.png) [@Machine\_Elf](https://boards.straightdope.com/u/Machine_Elf)\
**Post date:** [April 2, 2021, 2:02pm UTC](https://boards.straightdope.com/t/accuracy-of-no-touch-thermometers/939223/4 "2021-04-02T14:02:37Z")

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> [@carnivorousplant](#):
>
> We don’t poke things in each other’s face.

Can you ask someone else what their reading was when they scanned themselves? What about a warm computer component?

If your reading was consistently 97.8 before, and now it’s consistently 98.2, then it’s starting to sound (to me) like the thermometer might just be providing very coarse readings. The one I linked to includes the following in its manual:

> This thermometer is intended for scanning groups of individuals or monitoring an individual for elevated temperatures. It is not a substitute for a clinical thermometer. Always use a clinical thermometer when high accuracy body temperature measurements are required.

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**Author:** ![Dewey\_Finn](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/dewey_finn/32/4222_2.png) [@Dewey\_Finn](https://boards.straightdope.com/u/Dewey_Finn)\
**Post date:** [April 2, 2021, 2:08pm UTC](https://boards.straightdope.com/t/accuracy-of-no-touch-thermometers/939223/5 "2021-04-02T14:08:52Z")

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Going from consistent 97.8 to consistent 98.2 sounds pretty well calibrated. A Fluke page that came up in a Google search says, “ASTM requires that if you are going to use an IR thermometer for measuring skin temperature, it must be accurate to within ± 0.3 °C (±0.54 °F). That is just to ensure that it’s good enough to detect if a person’s temperature is different than what it should be, or if they have a fever.”

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**Author:** ![TriPolar](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/tripolar/32/3008_2.png) [@TriPolar](https://boards.straightdope.com/u/TriPolar)\
**Post date:** [April 2, 2021, 2:20pm UTC](https://boards.straightdope.com/t/accuracy-of-no-touch-thermometers/939223/6 "2021-04-02T14:20:07Z")

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I’m a little surprised it is consistently accurate to .4 °F for something so subject to the inconsistencies of human application, and humans themselves, but I’ve seen cheapo versions work with pretty consistent results. I might be a little more concerned that it reads so consistently on you since my own temperature varies in readings that much daily.

I’d also be checking that the lens is being cleaned properly. Or making sure it’s being cleaned at all because a little smudge from handling while changing the batteries would be a good way to get such a consistent change in readings.

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**Author:** ![Machine\_Elf](https://avatars.discourse-cdn.com/v4/letter/m/82dd89/32.png) [@Machine\_Elf](https://boards.straightdope.com/u/Machine_Elf)\
**Post date:** [April 2, 2021, 2:23pm UTC](https://boards.straightdope.com/t/accuracy-of-no-touch-thermometers/939223/7 "2021-04-02T14:23:03Z")

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> [@carnivorousplant](#):
>
> How accurate are these thermometers, and is there a way to calibrate them?

What’s the model of your thermometer? We can look up the manual for details.

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**Author:** ![carnivorousplant](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/carnivorousplant/32/3563_2.png) [@carnivorousplant](https://boards.straightdope.com/u/carnivorousplant)\
**Post date:** [April 2, 2021, 5:31pm UTC](https://boards.straightdope.com/t/accuracy-of-no-touch-thermometers/939223/8 "2021-04-02T17:31:27Z")

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I thought I looked for a manual when this issue came up. My boss is 98.7, so the damn thing works. Still no info on calibration.  
Such a device only need measure 95F-100F, anything else and the guy is sick and needs more than Mama taking his or her temperature.  
[https://www.jensentools.com/product/pdf/simzo%20hw-f7.pdf](https://www.jensentools.com/product/pdf/simzo%20hw-f7.pdf)  
The manual says to hold it 5cm away. The pharmacy nurse slides it over touching my forehead. The nurses at work hold it 5 cm away, curse about the reading and stick it in my ear.

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**Author:** ![Dewey\_Finn](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/dewey_finn/32/4222_2.png) [@Dewey\_Finn](https://boards.straightdope.com/u/Dewey_Finn)\
**Post date:** [April 2, 2021, 5:34pm UTC](https://boards.straightdope.com/t/accuracy-of-no-touch-thermometers/939223/9 "2021-04-02T17:34:38Z")

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> [@carnivorousplant](#):
>
> My boss is 98.7, so the damn thing works. Still no info on calibration.

Do you think it’s a problem that your temperature reads as 98 degrees plus or minus 0.2 degrees? It’s not; not everyone has the same normal body temperature and in any case, the temperature being read on your forehead is different from body temperature.

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**Author:** ![carnivorousplant](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/carnivorousplant/32/3563_2.png) [@carnivorousplant](https://boards.straightdope.com/u/carnivorousplant)\
**Post date:** [April 2, 2021, 5:49pm UTC](https://boards.straightdope.com/t/accuracy-of-no-touch-thermometers/939223/10 "2021-04-02T17:49:14Z")

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My problem is that it is always 97.2 with this device. I would believe it would be different when I walk in from 20 degree weather than when it is in the 70s.

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**Author:** ![Machine\_Elf](https://avatars.discourse-cdn.com/v4/letter/m/82dd89/32.png) [@Machine\_Elf](https://boards.straightdope.com/u/Machine_Elf)\
**Post date:** [April 2, 2021, 6:31pm UTC](https://boards.straightdope.com/t/accuracy-of-no-touch-thermometers/939223/11 "2021-04-02T18:31:20Z")

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> [@carnivorousplant](#):
>
> I thought I looked for a manual when this issue came up. My boss is 98.7, so the damn thing works. Still no info on calibration.  
> Such a device only need measure 95F-100F, anything else and the guy is sick and needs more than Mama taking his or her temperature.
> 
> [jensentools.com](https://www.jensentools.com/product/pdf/simzo%20hw-f7.pdf)
> 
> ### [simzo%20hw-f7.pdf](https://www.jensentools.com/product/pdf/simzo%20hw-f7.pdf)
> 
> 1851.21 KB
> 
> The manual says to hold it 5cm away. The pharmacy nurse slides it over touching my forehead. The nurses at work hold it 5 cm away, curse about the reading and stick it in my ear.

Page 2 says the accuracy is plus/minus 0.4F. Page 3 says the display has a resolution down to 0.1F, but that may well literally be describing what the digital display can do, and not the math going on in the signal processing system. It’s entirely possible that it will only ever show temps of 97.8, 98.2, or 98.7, but not anything in between.

On a related note, I found this:

> **[A brief report on the normal range of forehead temperature as determined by...](https://pubmed.ncbi.nlm.nih.gov/15877017/)**
>
> Our study shows that commercially available, handheld infrared thermometers require individual validation. Forehead temperature in excess of 35.6 degrees C is suggestive of fever. Further studies are required to confirm accuracy of this value in...

Figure 2 was of interest to me. The mean forehead temp among 1000 healthy adults was about 33.5C, or 92.3F. So at 89F, I’m closer to normal than I thought. OTOH, they claim a forehead temp in excess of 35.6C (96F) may be suggestive of a fever. How ya feelin’ these days?

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**Author:** ![carnivorousplant](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/carnivorousplant/32/3563_2.png) [@carnivorousplant](https://boards.straightdope.com/u/carnivorousplant)\
**Post date:** [April 2, 2021, 7:02pm UTC](https://boards.straightdope.com/t/accuracy-of-no-touch-thermometers/939223/12 "2021-04-02T19:02:37Z")

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Fine, thank you.

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**Author:** ![carnivorousplant](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/carnivorousplant/32/3563_2.png) [@carnivorousplant](https://boards.straightdope.com/u/carnivorousplant)\
**Post date:** [April 2, 2021, 7:43pm UTC](https://boards.straightdope.com/t/accuracy-of-no-touch-thermometers/939223/13 "2021-04-02T19:43:45Z")

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I can not remember if the intermediate temperature is 98.6 or 96.8.  
Some guy in seventeenth century France lined up 500 people and stuck a thermometer under their armpits.

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**Author:** ![DPRK](https://avatars.discourse-cdn.com/v4/letter/d/4491bb/32.png) [@DPRK](https://boards.straightdope.com/u/DPRK)\
**Post date:** [April 2, 2021, 8:38pm UTC](https://boards.straightdope.com/t/accuracy-of-no-touch-thermometers/939223/14 "2021-04-02T20:38:00Z")

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> [@Machine\_Elf](#):
>
> I have **[an IR thermometer](https://www.manualslib.com/manual/114639/Omega-Os540.html)** (not made for measuring body temp) with a claimed accuracy of plus/minus 3.6F in the range of body temperature, but when I measure my forehead it comes back with 89F. Hypothermia is defined as a body temp \<95F, and I feel fine, so it seems unlikely that my body temperature is in the range of 85.4-92.6F. I wonder if non-contact forehead thermometers are calculating some kind of adjustment from _actual_ forehead temperature to come up with a number that compares in a useful way with oral/rectal/subbrachial measurements.

If you point a thermometer at your skin, it will measure your skin temperature, not your core body temperature. What did you expect? As for accuracy and calibration, according to the instructions for a couple of handheld IR thermometers I have, you can set the assumed emissivity of the target surface, which is basically a coefficient for how efficiently it radiates thermal energy. The Wiki page says that “Skin, Human” is 0.97 to 0.999.

Now the accuracy of a fraction of a degree should be good enough for use on humans, whose temperature varies and fluctuates by at least that much anyway, but you still need to know what forehead temperature is normal compared to oral/rectal/axillary… Skin temperature will depend on factors like where you point it, let’s assume forehead, whether the person has been exercising, etc. I would not a priori expect an accuracy of better than a degree or so. I get a reading of 31-32 C pointing a thermometer at my arm, which seems about right.

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**Author:** ![Machine\_Elf](https://avatars.discourse-cdn.com/v4/letter/m/82dd89/32.png) [@Machine\_Elf](https://boards.straightdope.com/u/Machine_Elf)\
**Post date:** [April 3, 2021, 1:23am UTC](https://boards.straightdope.com/t/accuracy-of-no-touch-thermometers/939223/15 "2021-04-03T01:23:24Z")

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> [@DPRK](#):
>
> If you point a thermometer at your skin, it will measure your skin temperature, not your core body temperature. What did you expect?

I expected something in the neighborhood of what I reported for myself. That’s why I was very surprised that the OP was reporting 98.2F, a temperature more closely associated with oral/rectal/axillary measurements.

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**Author:** ![Richard\_Pearse](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/richard_pearse/32/13144_2.png) [@Richard\_Pearse](https://boards.straightdope.com/u/Richard_Pearse)\
**Post date:** [April 3, 2021, 1:34am UTC](https://boards.straightdope.com/t/accuracy-of-no-touch-thermometers/939223/16 "2021-04-03T01:34:31Z")

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What use would an external body thermometer be if it wasn’t calibrated to approximate an internal reading?

It measures your surface temperature and adjusts to give a corresponding body temperature. It doesn’t need to be super accurate, it just needs to be consistent and to discern between fever and not fever.

FWIW our IR thermometer has a “surface temperature” setting and a “room temperature” setting, obviously it doesn’t actually change to the way it measures temperature, it just has a different bias for each setting.

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**Author:** ![Broomstick](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/broomstick/32/246_2.png) [@Broomstick](https://boards.straightdope.com/u/Broomstick)\
**Post date:** [April 3, 2021, 8:34am UTC](https://boards.straightdope.com/t/accuracy-of-no-touch-thermometers/939223/17 "2021-04-03T08:34:48Z")

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> [@Machine\_Elf](#):
>
> I have **[an IR thermometer](https://www.manualslib.com/manual/114639/Omega-Os540.html)** (not made for measuring body temp) with a claimed accuracy of plus/minus 3.6F in the range of body temperature, but when I measure my forehead it comes back with 89F. Hypothermia is defined as a body temp \<95F, and I feel fine, so it seems unlikely that my body temperature is in the range of 85.4-92.6F. I wonder if non-contact forehead thermometers are calculating some kind of adjustment from _actual_ forehead temperature to come up with a number that compares in a useful way with oral/rectal/subbrachial measurements.

The temperature of your actual skin is not the temperature of the interior of your body. Hence why oral and rectal thermometers are inserted into an actual body orifice. The unadjusted temperature of exposed human skin in a person without a fever is about 91 F, so your IR thermometer is telling you the truth. The handheld non-touch fever detectors that consistently give higher readings are, I’m assuming, adjusted for that fact, giving an estimated interior temperature based on the surface temperature.

Fun fact: this winter, with staff coming in from the cold outside, we had some trouble with trying to detect body temperature with the no-touch’s - the surface layer of forehead skin was chilled due to exposure to sub-zero cold. So they started taking the read from our forearms, which were protected by winter jackets. Now that it has warmed up we’re back to pointing them at foreheads.

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<div class="post-metadata">

**Author:** ![carnivorousplant](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/carnivorousplant/32/3563_2.png) [@carnivorousplant](https://boards.straightdope.com/u/carnivorousplant)\
**Post date:** [April 3, 2021, 12:43pm UTC](https://boards.straightdope.com/t/accuracy-of-no-touch-thermometers/939223/18 "2021-04-03T12:43:44Z")

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> [@Richard\_Pearse](#):
>
> What use would an external body thermometer be if it wasn’t calibrated to approximate an internal reading?
> 
> It measures your surface temperature and adjusts to give a corresponding body temperature. It doesn’t need to be super accurate, it just needs to be consistent and to discern between fever and not fever.

An interesting point.  
To answer an earlier question, the thermometer display tenths of a digit, but is only accurate within .4 degrees F.

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**Author:** ![DPRK](https://avatars.discourse-cdn.com/v4/letter/d/4491bb/32.png) [@DPRK](https://boards.straightdope.com/u/DPRK)\
**Post date:** [April 3, 2021, 2:24pm UTC](https://boards.straightdope.com/t/accuracy-of-no-touch-thermometers/939223/19 "2021-04-03T14:24:24Z")

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If the thermometer displays some sort of “adjusted” temperature, not only would I expect it to say so in the instructions, it seems it should specify “point only at forehead” or something like that. I just did another little test and the thermometer read about 32 when pointed at the inside of my wrist, but 33-33.5 from the forehead.

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<div class="post-metadata">

**Author:** ![carnivorousplant](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/carnivorousplant/32/3563_2.png) [@carnivorousplant](https://boards.straightdope.com/u/carnivorousplant)\
**Post date:** [April 3, 2021, 3:22pm UTC](https://boards.straightdope.com/t/accuracy-of-no-touch-thermometers/939223/20 "2021-04-03T15:22:30Z")

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Perhaps the forehead temperature is more indicative of body temperature due to the pressence of blood vessels more near the skin than over body areas. Mama Plant alwas place her palm om my forehead to see if I have fever.

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