Core Body Temperature for Research

caleraresearch | Core Body Temperature Monitor

This article describes caleraresearch, our core body temperature monitor for researchers. calera is the technology developed by greenteg that enables monitoring of the core temperature with a wearable device. We have integrated calera into CORE, our product for athletes, and caleraresearch, our premium product for researchers.

Why monitor core body temperature for your research applications?

  • Core Body Temperature is a vital parameter for monitoring an individual’s health status and refers to the body’s organs’ temperature. It fluctuates following physiological processes, such as physical activity, circadian and ovulation rhythm, or various illnesses and sleeping disorders.

  • Before calera, it was only possible to accurately monitor the core temperature in study participants using invasive methods such as uncomfortable rectal thermometers or expensive ingestible pills. The non-invasive caleraresearch makes monitoring of the core temperature straightforward and manageable.

  • Other devices on the market try to estimate core body temperature via skin surface temperature. Due to the complexity of thermal regulation and the thermal influences from changing environmental conditions and physical activity, this estimate does not come close to calera’s accuracy and reliability.

  • What about in-ear (tympanic) and oral thermometers? These methods can provide accurate results during stable conditions like in a hospital bed. But these single-point measurements do not provide much information. The continuous temperature signal of calera will give much better insights.

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Why choose caleraresearch for your study?

As mentioned above, the calera technology is Accurate, Continuous & Non-invasive. We have integrated calera into caleraresearch and CORE. Both of these devices have the same hardware. But caleraresearch comes with services and functionalities that are designed specifically for researchers. caleraresearch is also compatible with all apps & tools developed for CORE.

CALERAresearch Hardware Characteristics

  • Compact: 50mm x 40mm x 8.35mm
  • Light: 17 grams
  • Rechargeable: yes, with a magnetic adapter
  • Battery life: 6 days constant monitoring (future upgrade to 15+ days)
  • Storage capacity: 84h of raw data (future upgrade to 10+ days)
  • Waterproof: up to 1.5m (IPX7)
  • Connectivity: Bluetooth Low Energy & ANT+
  • App support: PC / MacOS and compatible with CORE apps on: iOS / Android / WatchOS / Wear OS / Garmin ConnectIQ

Research Functionalities and Services of caleraresearch

For scientific studies, we recommend the use of CALERAresearch as it offers the following beneficial functionalities and services.

  • Raw Data Access

    • 1 Hz resolution
    • Core temp, Skin temp, Acceleration XZY, heart rate, and Heat-flux (1)
    • Run future algorithms on previously collected data
  • Remote Support

    • Assist before and during the study
    • Interpretation of data
    • IRB support
    • Check study proposal
  • Best Accuracy

    • Individually calibrated devices
  • Store Data on calera Research

    • No loss in data due to bad connection
  • PC / Mac Tool

    • Control multiple devices
    • Faster data download
  • CALERAresearch app designed for research and B2B application

caleraresearch can be used in regular mode or logging mode. In regular mode, it will behave like a CORE and upload core temp, skin temp, and heart rate (from an external device) with a 5-min resolution to cloud.corebodytemp.com. When using the logging mode, the raw data is saved locally on the device. All raw data is measured once per second, except for the core temperature, which is calculated every minute. The heat-flux sensor measures the amount of thermal energy that passes through the device and is the cornerstone of our technology.

(1) We can enable access to the heat-flux data after signing an agreement.

Furthermore, the raw data can be used to run future algorithms on previously collected data. As we keep on improving our algorithms and creating new algorithms for specific use-cases. this can improve the quality of your measurement without the need to do additional studies. This is especially important for edge cases, where currently, our algorithm has a lower accuracy than we strive for. E.g. firefighters, swimming, and hypothermia.

Only caleraresearch software allows to control multiple devices simultaneously. This tool is available for PC and Mac. Especially during large studies, we strongly recommend using this PC software instead of phone apps.

The caleraresearch app will continue to offer the features of the old CORE app. This app best suits researchers and B2B customers who require access to high-resolution raw data or simply want to see the live measurements without the bells and whistles of the new CORE app. For customers with logging mode access that want to control multiple devices simultaneously, we recommend using our PC/Mac software (the COREtool) that can be downloaded from the research download portal. (Password is available to customers). More information.

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caleraresearch applications

Core body temperature is an important vital sign. However, before CALERA, it was often impractical to measure the core temperature. Pulmonary artery catheters, urinary bladder, or oesophageal are only used in a medical setting because otherwise, the risks are too high. Rectal thermometers are often not preferred by participants, and ingestible thermometer e-pills are expensive and need the right timing. All other methods should not be used for scientific studies. A continuous core body temperature signal has countless applications, and we are working together with many partners and researchers in the fields below.

  • Physiology
  • Sports
  • Fever & Sepsis detection
  • Medical studies
  • Drug & Vaccine Testing
  • Ovarian Cycle
  • Thermal Comfort
  • Circadian Cycle
    • Sleep Disorders
    • Stress
    • Obesity
    • Alzheimer
    • Parkinson

caleraresearch received the Emergency Use Authorization in the US, making it available for clinical use during the Covid-19 crisis. We are currently filing for full FDA approval.

calera® validation

The accuracy depends on the use case and the reference thermometer method used. calera uses ingested electronic pills as the primary reference, which is a widely accepted solution for measuring accurate core body temperature.

The following charts show the accuracy of different thermometer types by Casa et al. and the CORE sensor data from the Verdel et al. study and greenteg's internal study. All data points are recorded during sports using a rectal thermometer as the reference method except greenteg's internal validation, which uses ingested electronic pills.

Casa et al. defined an accuracy threshold for the bias of 0.27° C. All studies with CORE showed that CORE/caleraresearch is well within this limit. greenteg's internal studies found a bias of 0.03 ° C. and Verdel et al. found a bias of -0.10 & 0.23 depending on the activity level.

The bias explains how precise a method is, meaning that the average of all measurements is close to the true measurement, but the spread of the error can still be significant. A better indication of the accuracy is the 95 % Limit of Agreement. This value shows that 95% of all measurements fall within this range from the bias. In the following chart, we show different thermometer types with respect to Limits of Agreement and include the CORE sensor data from the Verdel et al. study and greenteg’s internal study. Again, all points follow from measurements during sports and use a rectal thermometer as a reference, except our internal validation, which uses gastrointestinal pills.

Casa et al. (2007) work does not present a cut-off value for the limits of agreement, but Mogensen et al. [3] found that the limit of agreement from one of the best tympanic (in-ear) thermometer used in a medical environment is 0.8°C. [1,3] All values below this line should be considered highly accurate. Based on the data available, both from us and Verdel et al., caleraresearch is the most accurate non-invasive method for core body temperature measurements. (95% LoA CORE: Internal study 0.56°C, Verdel et al. 0.55°C and 0.61°C respectively).[2]

For more information about caleraresearch and its validation, please download the caleraresearch guide below.

In addition, a comparison of tympanic with core body temperature in stroke patients was performed by Ajčević et al. (2022) and reported in the Sensors journal. This work highlights the potential of core body temperature monitoring performed with greenteg’s technology as a method to track reliably stroke patients body temperature compared to standard temperature measurements. [4] Find out more here.

CALERAresearch guide

Do you want more information? Have a look at the caleraresearch guide. It describes:

  • How to use CALERAresearch
  • How to select different algorithms
  • Best practices
  • How to use the PC and phone software
  • How to read the export file
  • More validation results
  • caleraresearch accessories
  • caleraresearch app

Do you want to find out more about caleraresearch?

Contact us or Download our caleraresearch guide !

Yes, I want to download the caleraresearch presentation

Stay posted: We are releasing a major update to the caleraresearch guide soon!

CALERAresearch downloads

All documents and tools can be downloaded from here by CALERAresearch customers

Recommended readings to go further

  • Discover all the use cases related to our technology, here.
  • Explore our product line, here.


[1] Casa DJ, Becker SM, Ganio MS, Brown CM, Yeargin SW, Roti MW, Siegler J, Blowers JA, Glaviano NR, Huggins RA, Armstrong LE, Maresh CM. Validity of devices that assess body temperature during outdoor exercise in the heat. J Athl Train. 2007 Jul-Sep;42(3):333-42. PMID: 18059987; PMCID: PMC1978469

[2] Verdel, N.; Podlogar, T.; Ciuha, U.; Holmberg, H.-C.; Debevec, T.; Supej, M. Reliability and Validity of the CORE Sensor to Assess Core Body Temperature during Cycling Exercise. Sensors 2021, 21, 5932. https://doi.org/10.3390/s21175932.

[3] Mogensen CB, Vilhelmsen MB, Jepsen J, Boye LK, Persson MH, Skyum F. Ear measurement of temperature is only useful for screening for fever in an adult emergency department. BMC Emerg Med. 2018 Dec 3;18(1):51. doi: 10.1186/s12873-018-0202-5. PMID: 30509206; PMCID: PMC6276133.

[4] Ajčević, Miloš, et al. “A Novel Non-Invasive Thermometer for Continuous Core Body Temperature: Comparison with Tympanic Temperature in an Acute Stroke Clinical Setting.” Sensors 22.13 (2022): 4760.