Common Questions

Common answers about the CORE sensor


For most events - CORE is permitted to be used in training and competition. But alwys ensure that you are current with the latest regulations to ensure you still comply.


The current version 10.06.2021 UCI (Union Cycliste Internationa) Cycling Regulations states the following:

§ 4 Onboard technology
1.3.006 bis
Devices which capture or transmit the following physiological data are authorised: heartrate, body temperature, sweat rate. The authorisation is, however, limited to transmission protocols which enable only the rider concerned to view the data during a competition.


The ITU (International Triathlon Union) does not limit the use of core body temperature monitoring sensors during competition.


The IAAF (International Association of Athletics Federations) World Athletics Technical Rules (1. November 2019) states:

6.4 For the purpose of this Rule, the following shall not be considered assistance, and are therefore allowed:

6.4.4 Heart rate or speed distance monitors or stride sensors or similar devices carried or worn personally by athletes during an event, provided that such device cannot be used to communicate with any other person.


If your event is not listed and you are not sure or need more clarifications. Contact us and we will see if we can help clarify the ruling.

The CORE Body Temperature Monitoring sensor is similar to Heart Rate Monitor sensors in that it uses ANT+ and BLE and it paired to an athletes sport computer or watch and the data is only visible to them.

The CORE sensor is not a telemetry device. The CORE sensor is fastened securely to the heart rate monitor strap using the securing clips.

Women Using CORE

Chest straps are commonly used for heart rate monitors and the CORE sensor. However, some women find these chest straps uncomfortable. Thankfully, a number of alternatives allow the use of CORE without a chest strap:

  • Attach the CORE sensor to the bra band on (often attached upside down) or closer to the back. The black plastic clip can help secure the sensor.

  • Adhere the CORE sensor to the torso using the included medical-grade patches. Instructions for placement are found here, and replacements can be purchased from our store.

Wear the CORE sensor on your arm using an arm strap. Please note that accuracy can be lower than when CORE is positioned on the torso.

For sports usage, CORE needs data from a heart rate monitor for its algorithm to deliver the most accurate core body temperature. This heart rate data can come from a number of sources:

  • A traditional heart rate monitor that uses electrocardiography (ECG) sensors. This provides the most accurate data and is typically worn on a separate strap. However, we know a number of women who have sewn small sleeves on the front band of their sports bras to house the monitor. This allows full functioning of the monitor without the discomfort of a separate chest strap.

  • A PPG (photoplethysmography) heart rate monitor integrated into a smart watch. These monitors use light pulses to measure heart rate and are not as accurate as the ECG monitors. The CORE sensor will work with them, but the accuracy of temperature measurements may decline.

  • A PPG heart rate monitor worn on an arm band. While still not as accurate as an ECG sensor, the arm placement delivers much more accurate data than the wrist sensor.

24/7 monitoring

The CORE sensor can also be worn outside of sports activity without a heart rate monitor to continually track basal body temperature. Basal temperature can help predict fertility and provide an early indicator of pregnancy.

What are normal core body temperature ranges?

Well... it depends on your reference

A normal core body temperature range is between 97°F (36.1°C) to 99°F (37.2°C).

During the day, the temperature fluctuates and this is known as the Circadian Rhythm so the widely regarded temperature of 36.9ºC / 98.4ºF is a daily average and subject to variation.

During sport, the core body temperature can increase above 38ºC / 100.4ºF

Temperatures above 39ºC / 102ºF start to put the human body at risk of heat-stress although the training and conditioning of each individual means that the tolerance varies significantly.

What is reliable temperature measurement?

Different thermometer methods give different core body temperature readings.

Rectal thermometers, ingested e-pills and bladder and heart catheters are all invasive thermometers which are also considered to be accurate and hence are suitable for medical use.

Laser scanners, ear thermometers, oral thermometers and other skin temperature calculators are considered less accurate and consistent so the values delivered by a single device or in comparison to other thermometers can vary significantly. The temperature also varies on different parts of the body (for example, the extremities such as arms and legs can be cooler().

The CORE Body Temperature monitoring device is has been tested extensively using accurate rectal thermometers and e-pills as 'controls' to provide the same level of accuracy.

Why do you want to monitor your core body temperature?

Your core body temperature fluctuates during the day naturally and is impacted by activities such as sport or even just rises as you burn more calories.

Monitoring your temperature continuously can provide insights into your health status. For instance, you can track disease progression, ovulation, the circadian rhythm and even see the impact of jet lag.

Core body temperature is a vital sign so provides an indication for people working or doing sports when they are 'effective', when their performance will degrade and when they are are at risk of heat-stress.

Monitoring continuous provides immediate information as well as the 'big picture' to observe trends or discrepancies.

CORE Use in China

The CORE sensor works all over the world however and transmits live data to many different devices.

The CORE phone app can work in China but as the app uses a cloud database. That databased based on Google and at this time is not directly accessible in China.

To enable the CORE phone app to work properly in China a VPN service may be necessary.

If you need access to the Android CORE Phone App - please contact us.


For our US based customers:

  • COREmedical can be considered as a clinical thermometer under the Emergency Use Authorization in support of the current Public Health Emergency COVID-19
  • COREmedical can be used to measure core body temperature in both clinical and non-clinical settings

For all customers:

Please keep note that COREmedical is not FDA nor CE medical approved/cleared.

  • COREmedical is not intended to substitute a medical grade thermometer. However, COREmedical is an ideal supplement to routine medical grade temperature screenings, such as those conducted prior to admission, or dismissal from/to any facility, building or regulated public areas.

  • CORE should be used by healthy adults in a stable environment and is only meant to inform you about your overall wellbeing. No medical advice can be concluded from the measured temperature data, and it cannot replace the services of health professionals. Deviations from the normal temperature range should be investigated by a health care professional. Never disregard professional medical advice or delay in seeking it because of the temperature measurements by CORE.

To read the full disclaimer click here.

CORE sensor technology

How does CORE measure your core body temperature?


  • CORE uses a thermal energy transfer sensor from greenTEG in combination with a sophisticated AI algorithm to calculate the Core Body Temperature.

  • The AI algorithm calculates the Core Body Temperature with the medical grade accuracy.

  • Due to greenTEG's sensor, this technology has a high accuracy even in a not controlled environment (e.g. under the sun, during intense physical activity, and within a large range of ambient temperatures and humidity)

is the phone app needed to use core?

When you are wearing CORE, it will continue to broadcast record data internaly that can be downloaded later.

CORE has an internal memory which stores data, even when disconnected from the CORE App for Android or iOS. The next time you start your app and connect, the App will synchronise and load the metrics.

So the CORE phone app is a convient way configure and view data your CORE data but is not necessary to be present to use your CORE sensor.

If you are using another device such as a compatible Wahoo or Garmin cycle computer or watch, CORE must remain within range to record the core body temperature metrics to the FIT file.


Default mode: By default the CORE sensor is always on and on a single charge the battery will last for about 6 days. When the CORE sensor is not being worn, it is still on and consuming power.

Standby mode
has been re-enabled; this can give up to 1 month of battery life. This mode is enabled on the sensor settings from the CORE phone app. The CORE sensor will automatically turn on when it detects it is worn (we suggest shaking it and looking for the green flashing light) and it will turn off when it detects it is not receiving valid data (is not being worn) for a longer period.

If the CORE sensor is worn a lot, this consumes power and the time until a recharge is required is shorter.

Standby Mode

Standby mode is off by default and must be enabled via app settings. The basics:

  • when standby mode is enabled, CORE will automatically enter a low power state after it has not been worn for 20 minutes.
  • during standby mode, all data communication is disabled.
  • standby mode can extend the time between recharges to up to 1 month.

You can wake your CORE from standby mode by shaking the CORE, connecting it to a charger, or resetting it.


The LED light has six functions:

  1. battery level indication
  2. heart rate monitor detected
  3. charging status
  4. the device initially connects to CORE (4x rapid blink as previously)
  5. data is downloaded from CORE (continual fast blinking, as previously)
  6. on reset (short blink followed by battery level indication, as previously).


Shake to wake - battery level indication

When you shake your CORE to wake it from standby, the LED indicates how much battery is left.

LED behaviour


Residual capacity

Operating time left

Standby time left

3x short blink



Less than 12 hours

Less than 1 day

1x longer blink



> 12 hours

1–5 days

2x longer blink



> 36 hours

> 1 week

3x longer blink


>50 %

> 72 hours

> 2 weeks

Heart rate Monitor connection Indication

When the CORE is shaken, following the LED blinks that indicate the battery status, the LED will then indicate whether a heart rate monitor is connected for 2 minutes.

A single flash every two seconds indicates no heart rate monitor. In this case the CORE sensor using the 'low activity' mode

A double-flash every two seconds indicates that the CORE sensor is connected to a paired heart rate monitor and it is in the 'Sport activity' mode

Charging Indication

The green LED light will also now show charging status while connected to a USB:

  • charging: LED blinks 1s on/1s off
  • charge complete: LED off
  • connect USB: blink 5x
  • disconnect USB: no reaction

CORE connects to a device indication

Your CORE will blink 4x rapidly when it connects to a device.

Data downloaded from CORE indication

Your core will continuously blink rapidly while it is downloading data.

resetTING the CORE indication

The light will be solid for about 2 seconds following by the battery level indication flashing sequence.


CORE is waterproof and can be used while swimming.

After active sports and swimming we recommend rinsing CORE with clean water and soap. The medical-grade plastic case can also be disinfected using 70%-75% alcohol. Do not use acetone or 100% alcohol as these solvents will attack the plastic material or color print.

The specially design magnetic power cable means that the CORE device remains closed/sealed.


  • The thermal energy transfer sensors are manufactured on-location by our parent company greenTEG in Zurich, Switzerland.

  • The CORE housing (medical grade plastic) and circuitry is manufactured and assembled by our production partner company in the European Union and Asia.

What is CORE's service life

CORE is designed to withstand 10,000 hours of normal use.

For the best performance, store the CORE sensor in a cool location and try not to leave it without charge for extended periods of time.

Currently it is recommended to charge once per week. Following the planned July 2021 update, the deep sleep function will allow the CORE sensor battery (without active use) to run for three weeks before charging is recommended.

Testing Procedure

Following test conditions were defined by the customer:

  • Temperature: 60 °C
  • Humidity: 90% RH
  • Test Duration: 340 hours / 14 days + 4 hours

Other conditions:

  1. Device stays in operating state (ON) throughout the test
  2. Device must be recharged at T<40°C every 5 days (or less)

Device was put in “logging mode” throughout the test. “CL 1” was paired with a HR monitor to induce periodic ANT scan (increased power consumption)

Test was interrupted at day 4, day 9 and day 12 to recharge the devices and download logging data.

Length of data log was limited to 3.5 days due to the size of the internal storage of the DUT. DUT integrity was verified periodically by connecting to the DUT via CORE app and noting the battery voltage value.

No Signs of corrosion of the charging pins

Measurement Equipment

  • Climatic Test System Vötsch 4006
  • Temperature deviation in time: +/- 1K
  • Temperature deviation in space: +/- 2K
  • Humidity deviation in time: +/- 5% RH max


DUTs were put in the main chamber of the climatic test system together with a Sensirion SHT21 combined thermometer / hygrometer (precision +/- 0.3°C and +/- 2% RH) to supervise and validate set temperature and humidity.

Measurement Data

Data and Images available upon request.

CORE firmware Changelog

0.7.2 (2022-03-01)
  • Fixes excessively high temperature readings at the beginning of a workout.
0.7.0 (2022-02-02)
  • Smart algorithm switching
    • CORE automatically switches to low activity algorithm when approriate (rest, sleep), even when heart rate monitor is paired.
  • Last 4 digits of CORE ID added to the device name
    • In app device scan, device will show up as "CORE 3A:5F" instead of "CORE"
    • Facilitates identification of unkown devices under iOS
    • Note: Only applies if no nickname is set
  • Adaptions to Bluetooth Health Thermometer Profile (HTP)
    • Extention of Device Information Service to fully comply with HTP
    • only relevant for developers - see this link and this link or contact us for details
0.6.2 (2021-12-23)
  • Adaptions to Bluetooth temperature profile
    • only relevant for developers - see this link or contact us for details
  • Adaptions to ANT profile
    • only relevant for developers - see this link or contact us for details
0.6.0 (2021-09-24)
  • Adapted LED feedback:
    • Battery state of charge indication upon shaking core
    • Adapted blink pattern to indicate heart rate monitor connection status
    • "slow blink" pattern when core is charging
  • Standby mode support (Requires CORE app 1.3.5): Increases time between re-charges to up to 5 weeks
  • Bugfix: ANT connection logic leading to heart rate re-connection problems
  • Shaking CORE leads to an addictional scan for heart rate monitors
0.4.1 (2021-06-21)
  • Improved handling of bad heart rate signal
  • Data quality as low in case of extreme jumps in HR signal
  • Intermediate better support on Wahoo bicycle computers
0.4.0 (2021-05-26)
  • Activity algorithm dynamic switching without necessary algorithm reset:
    This is a big change internally when transitioning between the 24/7 Everyday Living algorithm and the Sports Algorithm (with heart rate monitor)
  • Bugfix: Guard against sports algorithm rare crash (scaled feature)
  • Improved "cold start" for greater initial accuracy
  • Heart Rate values < 30 are now regarded as invalid
  • Proper rounding for skin_temp in ANT CORE profile
0.3.20 (2021-04-23)
  • Set data quality to 0 if charger is plugged-in
  • Reset CoreTemp and quality when leaving a measuring mode
  • Miscellaneous internal bug fixes
0.3.19 (2021-03-24)
  • Update on data quality 0 is used
  • Always save history independent of quality (before: only saved if quality>0)
  • Continuously update BLE health thermometer profile core body temp value
    • send notifications if enabled
    • transmit IEEE11073-NaN if quality == 0
  • Research mode channels fields logging updated
  • Server unit calibration settings verified and synced properly
0.3.18 (2021-03-10)
  • Auto-fix too many paired Heart Rate monitors bug at firmware startup
  • Updates to the research mode functionality
0.3.17 (2021-02-17)
  • Add standard BLE battery profile
  • Run ANT Heart Rate monitor search after new device paired or new measurement started
  • ANT Core profile: page0 HR status now indicates active HR connection (instead of 'min. 1 device paired')
  • Miscellaneous internal bug fixes
0.3.16 (2021-02-04)
  • Quality score in no-sports mode now based updated to more relevant value
  • ANT Core profile
    • allow pairing with wildcards
    • handle page70 requests for pages 0 and 1
    • transmit correct ANT page0 HR source status
    • HR pairing via ANT
0.3.15 and earlier
  • Prior change logs available upon request