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To what degree can you trust different thermometers

7 Types of Thermometers and to what Degree You Should Trust Them

By Dr Justin Smith (MD)

Generally, I’m not too concerned about the exact number of your child’s temperature. “Felt warm” is usually more than enough for me to know my kid has a fever.  But, like many things in medicine, that has changed in the world of COVID-19. Many of the protocols for screening and testing have been developed based upon knowing if you or your child has a fever. So, now more than ever, knowing which type of thermometer and the best way to take your temperature is crucial. Here is a look at 7 different types of thermometers (and a bonus one that many of you swear by) and how to decide if they are right for your family:

1. Forehead strips

Ahh…the allure of not having to wake your baby up to know their temperature. Sounds nice, right? And it might even offer you some peace of mind. But is that peace of mind false? Probably. There aren’t many studies on the use of strip thermometers but most recognize the accuracy of detecting fever at around 35 to 50 percent. What does that mean? If you don’t want to touch your child and wake them up to see if they have a fever, just flip a coin…Heads=fever, Tails=no fever.

2. Wearable thermometers

Trying to one up the forehead strips is the wearable thermometer. In theory, it will notify you via an app if your child’s temperature reaches a fever. Like the forehead strips, the accuracy of these is suspect. On top of that, if you’ve read anything I’ve written about fever before (like this post about fever myths), you might know that I don’t think it’s important to know your child’s temperature every second of the night.

3. Pacifier thermometers

Just plain “Nope.” They don’t work. Save your money.

4. Ear thermometers (tympanic)

Now we’re getting into the more common and reliable ways of checking your child’s temperature. While not my favorite, some parents like the relative ease of the tympanic thermometer. This thermometer is placed in the ear. A few important points: 1) It can’t be used in children under 6 months. 2) Placement in the canal matters. Read the directions and follow them. 3) Excess earwax can cause an incorrect reading.

5. Forehead thermometers (temporal)

This is the preferred method for most kids 3 months and over, particularly for screening when you can’t or prefer not to do a rectal temperature. That’s why you’ll find most doctor’s offices using them at check-in. Once again, the placement and the way you move it matters so follow the directions included. If you are getting a reading that doesn’t make sense, check it a few more times until you are getting consistent readings. Another nice thing about these thermometers is that they can be used for screening even before 3 months of age…before you go to take a rectal temperature.

6. Digital thermometers

A nice digital thermometer is good to have because it can be used throughout age ranges, provides accurate readings, and it’s cheap.

At any age, you can use a digital thermometer under the arm and add 1 degree to get a general sense of what the true temperature might be (just don’t count on that as 100-percent reliable.)

Before age 3, the most accurate temperature will be a rectal temperature, in the bottom (see below for how to take a rectal temperature). Anything over 100.4 taken rectally is a fever. After age 4 or 5, you can start to take the temperature in the mouth (see below for how to take an oral temperature). I general consider 101.4 or above to be a fever when taken orally.

7. Non-contact Infrared Thermometers

With the recent events related to COVID-19, I’ve gotten a lot of questions about these thermometers. They are an option for you because they are accurate, can be used for screening at your home or office and they don’t require touch.

Bonus: Mom’s hand or lips

“He feels about like the oven which is set at 350 degree.” Actual phone call. Actual quote.

Ok, this is not an actual thermometer, but I thought it deserved a mention. While touching the child might give you an idea that you should check a temp, mom’s hand is not a reliable way to determine the child’s temperature. Now grandma’s hand…I find it best not to argue with grandmas. “It felt like 102…yes ma’am.” But seriously, use an thermometer that works.

Hopefully this article will provide you some guidance for the next time you need to replace your thermometer. You have a few solid options and a few terrible ones. Some are basic but work just fine. Some have fancier features that might be useful. Others have stuff which prove that the solution to fever is not always more (cow)bells and whistles.

How to take a rectal temperature

  • Clean the thermometer with soap and water.
  • Place a small amount of petroleum jelly on the end.
  • Place your baby across your lap face down or on their back on a firm surface.
  • Gently place the thermometer about ½ inch into the anus.
  • Place your entire hand around the child’s bottom, holding the thermometer in place between your fingers.
  • Hold in place for about 1 minute or until you hear the beep.

How to take an oral temperature

  • Wait 10-15 minutes after the child has had a drink.
  • Clean the thermometer with soap and water.
  • Turn the thermometer on and place under the tongue toward the back of the mouth.
  • Wait for 1 minute or until you hear the beep.

Get to know Justin Smith, M.D.

Justin Smith, M.D., is a pediatrician in Trophy Club  and the Medical Advisor for Digital Health for Cook Children’s in Fort Worth, Texas. He has an active community on both Facebook and Twitter as @TheDocSmitty and writes weekly for Cook Children’s checkupnewsroom.com. He believes that strategic use of social media and technology by pediatricians to connect with families can deepen their relationship and provide a new level of convenience for both of their busy lifestyles. Dr. Smith’s innovative pediatric clinic, a pediatric clinic “designed by you,” open now. Click to learn more. To make an appointment, call 817-347-8100.



The Centre for Evidence-Based Medicine develops, promotes and disseminates better evidence for healthcare.

Accuracy of strip-like forehead thermometers

March 18, 2020

Strip thermomenters are not accurate

Jon Brassey, Carl Heneghan

Oxford COVID-19 Evidence Service Team
Centre for Evidence-Based Medicine, Nuffield Department of Primary Care Health Sciences
University of Oxford

Lay Summary by Mandy Payne, Health Watch

Verdict: If peripheral thermometers are used they will not detect a fever in about 4 in every 10 children with one.  Peripheral thermometers should not be relied on by clinicians to influence clinical decision making. If there is no alternative, consider the actual temperature measurement will be at out by at least +/-1.5°C and ask for repeated measurements.

Young Children

In young children the advice is straightforward and is found in NICE’s recent guideline on in the under 5s where they state:

1.1.5 Forehead chemical thermometers are unreliable and should not be used by healthcare professionals.”


For children generally (as opposed to just the under 5s) the evidence appears variable! The earliest paper we found was “An Evaluation of a Plastic Strip Thermometer” which reports “We conclude that the Clinitemp is unacceptable as a substitute for the mercury/glass thermometer.” In the same year, a smaller study (n=134) reported: “Parents who rely on these strips to identify a fever in their children may be misled by an erroneous afebrile reading.”

1996 study with 120 patients (20 in each of six age groups: < 1 month, 1 to 5 months, 6 to 11 months, 12 to 23 months, 2 to 14 years, and adults concluded: that previous studies have all used inappropriate methods of analysis….. Forehead strip thermometers are easy to use, but they do not estimate the rectal Temperature as accurately as the axillary Temperature does.”

A more recent cross-sectional  2018 study of 995 children found that temporal measurement of temperature is not recommendable, but the ear measurement proved useful for screening purposes, especially among children aged six months to 5 years.

Children and Adults

Three reviews were found with the earliest being the 2010 RACGP review which concluded:

“The digital thermometer provides the best agreement with the mercury in glass thermometer. The infrared tympanic thermometer may be a preferable option for the uncooperative patient. The liquid crystal forehead thermometer is best used at home.”

In 2012, Healthcare Improvement Scotland produced a technology scoping report that found:

  • Evidence from a range of adult and paediatric patient groups suggests that temporal artery thermometers are insufficiently accurate for clinical use in inpatient settings

Six studies compared both temporal artery thermometers (TAT) and infrared in-ear thermometers four studies favoured TAT.

infrared in-ear thermometers

A 2015  systematic review of  75 studies (n = 8682) on the accuracy of Peripheral Thermometers for Estimating Temperature reported that most studies at high or unclear risk of bias. The main results were:

  • Peripheral thermometers had pooled 95% limits of agreement outside the predefined clinically acceptable range (± 0.5 °C),
  • Especially among patients with fever (-1.44 °C to 1.46 °C for adults; -1.49 °C to 0.43 °C for children)
  • For detection of fever, sensitivity was low 64% but specificity was high (96% [CI, 93% to 97%]; I2 = 96.3%; P < 0.001).

Limitations: High-quality data for some temperature measurement techniques are limited. Pooled data are associated with interstudy heterogeneity that is not fully explained by stratified and metaregression analyses. Their performance may be improved by taking repeated measurements over time, and they can be useful for measuring Temperature in children while they are sleeping.


We found a single study in 201 only adults in ICU that reported the compact digital axillar thermometer and the digital thermometer with probe obtained the highest overall valuation score.

Disclaimer:  the article has not been peer-reviewed; it should not replace individual clinical judgement and the sources cited should be checked. The views expressed in this commentary represent the views of the authors and not necessarily those of the host institution, the NHS, the NIHR, or the Department of Health and Social Care. The views are not a substitute for professional medical advice.