CALERA is the technology behind CORE and was developed by greenteg. For researchers we created CALERA Research that comes with functionalities and services tailored for scientific studies. The consumer version of the CORE sensor already allows customers to download core temperature, skin temperature and the heart rate values from the CORE Cloud web app with a resolution of 5 minutes. Customers using sports devices can access this data recorded to the FIT file at a resolution of 1 minute.

CALERA Research will give you access to high-resolution (1Hz) raw data; Core Temperature / Skin Temperature / Heart Rate (Ext.) / Accelerometer and Heat-Flux*. This data is stored locally on the device. The devices are individually calibrated to ensure the highest possible accuracy, and we offer our expert support to help you setting up your studies and interpret the results.

*Heat-Flux is available on agreement. Please contact us, we would be glad to provide guidance regarding the suitability of the CALERA Research solutions for your project.





Core body temperature which has been traditional impractical to measure in real-time with a high level of accuracy for practical applications. Pulmonary artery catheters, urinary bladder, or oesophageal are almost only used in a hospital setting. Rectal thermometers are often not preferred by participants, and ingestible thermometer e-pills are expensive and need the right timing. Other thermometers do not allow for continuous and/or accurate monitoring.

Monitoring real-time core body temperature has countless applications, and we work extensively across a number fields already. If you have an application, we would be happy to discuss this with you further.

  • Thermo-physiology
  • Sports
  • Fever & Sepsis Detection
  • Covid-19
  • Drug & Vaccine Testing
  • Ovarian Cycle
  • Thermal Comfort
  • Circadian Cycle
    • Sleep Disorders
    • Stress
    • Obesity
    • Alzheimer
    • Parkinson

Note: The CORE sensor has provisional FDA approval under the Covid-19 provisions for use in the United States of America. The filing for the full FDA approval in in progress.

Application examples

Circadian cycle

The simplest way to monitor the circadian cycle is to measure the core body temperature. The temperature can be measured easily with CALERA Research without having a significant impact on the subject's daily routines. Changes in the circadian cycle can help to draw conclusions about health issues like jetlag, narcolepsy, insomnia, sleep quality, burnout, Alzheimer’s, Parkinson’s, ovulation status, and many more.


During high physical activity, your core temperature can rise to dangerous levels. Professional athletes have embraced CORE enthusiastically for protection, heat adaption training and strategical decisions. Many Olympic athletes and UCI riders describe the device as a game changer. We also want to bring this technology to researchers to develop more insights in physiology. During high physical activity a heart rate monitor is connected to CORE to increase the accuracy.

Fever monitoring

Fever changes the thermoregulation of the body and requires sophisticated algorithms to detect the temperature accurately. The figure to the left shows that the algorithm fits the reference method very well. Indicated are also tympanic temperature measurements (orange diamonds) and intakes of 500 mg paracetamol (dashed lines).


The accuracy is dependent on the use-case and on 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 shows the accuracy of different thermometer types by Casa et al. [1], as well as the CORE sensor data from the Verdel et al. [2] study and greenTEG`s internal study. All datapoints are recorded during sports using a rectal thermometer as the reference method with the exception of greenTEG`s internal validation which uses ingested electronic pills.

Casa et al defined an accuracy threshold for the bias of maximum 0.27° C. All studies with CORE showed that CORE/CALERA Research 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 large. A better indication of the accuracy is the 95 % Limit of Agreement. This value shows you that 95% of all measurement fall within this range from the bias. In the next chart we show different thermometer types with respect to Limits of Agreement, and also 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. 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 aurial (in-ear) thermometer used in a medical environment is 0.8° C. All values below this line should be considered highly accurate. Based on the data available, both from us and Verdel et al., CORE should be considered the most accurate non-invasive method for core body temperature measurements. (greenTEG = 0.56° C, Verdel et al. 0.55 ° C & 0.61 ° C)


Feel free to contact us and discuss your study and the implications your use-case has on the accuracy.

Thermometer methods

As your core temperature is not uniformly distributed in your body, various thermometer methods react differently to external and internal thermal influences. It is therefore important to always keep the thermometer method in mind when reading about study results. As CALERA Research’s algorithm is mainly based on ingestible pill data it will also behave most similar to this method. Have a look in the papers below where the differences between these methods are discussed.


Esophageal vs. rectal probe vs. telemetric pill

Esophageal vs. rectal probe  

Rectal probe vs. telemetric pill

Rectal probe vs. Tympanic temperature


[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.

[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] Gosselin, J.; Béliveau, J.; Hamel, M.; Casa, D.; Hosokawa, Y.; Morais, J.A.; Goulet, E.D.B. Wireless Measurement of Rectal Temperature during Exercise: Comparing an Ingestible Thermometric Telemetric Pill Used as a Suppository against a Conventional Rectal Probe. J. Therm. Biol. 2019, 83, 112–118.