CORE Review | pro-Athlete, Skin+Core Temp Sensor by greenTEG

Core Review greenTEG Body Temperature Sensor
CORE Review | pro-Athlete, Skin & Core Body Temperature Sensor by greenTEG

This is a detailed review of the CORE Body Temperature Monitor which focusses on making accurate skin & core temperature readings. The company, greenTEG, has many uses planned for this sensor including for patient and workplace monitoring. However I’m interested in the pro-Sports Performance side of greenTEG’s business and the sports use-cases are now nicely integrated into the Garmin environment with more to come from wider ANT+ support, Wear OS support and the opening up the code to interested 3rd parties.

The CORE Monitor was announced in August 2020 and I am reviewing the tweaks, updates and clarifications for 2021. I’ll cover all that further below. To start with, here is a summary

Core Review greenTEG Body Temperature Sensor
  • Price - 80%
  • Apparent Accuracy - 99%
  • Build Quality & Design - 90%
  • Features, Including App - 90%
  • Openness & Compatability - 90%


It’s a pleasure to use products that have been well designed and this is one of them. Core looks good but, more importantly, it’s compact in size, comfortable and easily attaches to a chest strap heart rate monitor. Sure, Core can be worn in other ways too but that strap method is what most of us will use.

Core greenTEG Body Temperature SensorThe iOS app is nicely designed too and gives a good, clean and focussed user experience where the key CORE and SKIN temperature can be graphed alongside a paired heart rate sensor. Perhaps a data export option on the app would please some but the reality is that most people buying the CORE for sports will be using it with a Garmin watch or Garmin bike computer. Google’s Wear OS, Apple’s Watch OS and Wahoo might all come into the game somewhere but only on the peripheries.

For now, the Garmin CIQ experience is more than good enough and the data field and widget both work well to give you the data where you need it and to record it into your workout FIT files. In the not too distant future, we will get native body temperature support in the ANT+ specification, couple that support with Bluetooth access and the product will be truly ‘open’.

UCI team Bora-Hansgrohe use the product now and other pro-level athletes will follow suit across a wide range of sports where elevated body temperatures are known to negatively impact performance. This tech has already spread to researchers in a variety of disciplines and to wannabe athletes, perhaps like you and me! Eventually, it will be used by concerned parents of newborns with a temperature. This product appears to be continuously accurate and claims accuracy to +/-0.21 degree Celsius and is wholly non-invasive, bits just don’t need repeatedly sticking in anywhere unpleasant!



  • Ground-breaking sports tech for serious athletes
  • Nails the Garmin experience
  • Appears to be accurate & actionable
  • Can be sold as a clinical thermometer
  • Useful to validate heat adaptation protocols
  • Useful to be alerted to and address heat stress
  • Wider adoption of temperature data is more likely than complex data (SmO2).


  • Will become detached from chest straps without the clip (included).
  • Needs native ANT+ support, can be recorded as tHb in the ANT+ Muscle Oxygen profile
  • Needs Apple Watch support
  • The USB charger can easily become detached,
  • Cannot be used for medical/diagnostic purposes
  • Off-body detection needs improving (wear it in advance of training)

 Core Review greenTEG Body Temperature Sensor

CORE Body Temperature Monitor – What’s Included?

You get the CORE device and a custom-USB charging cable that is magnetic. I also got 8x adhesive patches but haven’t used them.

There are 4x small black clips. These are very important as they stop the CORE becoming accidentally detached from your HRM strap.

CORE Body Temperature Monitor Review – How does it work

CORE is a Heat Flux and that Wiki link explains how the tech works, although CORE themselves prefer the term Thermal Energy Transfer.

You pair Core to your iOS/Android app as normal but then it gets more nuanced as you also use the app to pair your HRMs directly to CORE. Then, CORE caches SKIN TEMPERATURE and CORE TEMPERATURE and broadcasts the same data over ANT+ and BLE. Interestingly CORE has two algorithms, both have the same once-a-minute frequent data but the data is more accurate for intense efforts if an HRM is present. Think of it as a sports mode and a 24×7 mode where the presence of an HRM automatically enables sports mode.

Here is how the data is currently transmitted

  • ANT+ as proprietary data for CORE’s CIQ Data Field
  • BLE standard health thermometer profile
  • ANT+ over the tHb channel (Muscle Oxygen)
  • Future: It looks likely that the ANT+ TEMPERATURE Profile is being modified to add SKIN and CORE temperatures alongside the existing environmental temperature. Ie It will become a native ANT+ piece of data.

So, as of January 2021, you can collect your data in several ways namely the CORE app, any Garmin device that supports CIQ2.4 or above (generally, 735XT and Edge 820 onwards) or devices like Wahoo ELEMNT Bolt that supports tHb/SmO2 data.

There is a Wear OS app very close to launching that’s already on the Google Play store and Apple Watch OS will be supported after that along with the release of interface information for 3rd party developers.

In reality, all of this condenses down to “Yes. your high-end Garmin devices will be able to capture this data and, yes, you can leave the smartphone app at home. No, the cached data can’t be retrieved by your Garmin

CORE on Garmin CIQ

CORE produces both a CIQ DATA FIELD and CIQ WIDGET for Garmin. You know what the data field is going to do, however, the WIDGET is unusual. The widget replaces some of the functionality in the Garmin Connect APP/Garmin Express and allows you to specify the ANT+ device number as well as setting an alert temperature; the widget can also be used to show a live large-font display of temperature without starting a workout.

Core greenTEG Body Temperature Sensor for skin


Here we have some images of the Garmin functionality on the new Garmin Enduro. The widget gives a nice full-screen temperature reading if that’s what you want but more importantly allows you to change the temperature alert value on the watch. Perhaps athletes will more often use the data fields which can be easily added on most Garmin watches.

Note: For a CIQ data field you do NOT pair the CORE as an ANT+ sensor, the widget/data field automatically do that and hence the need for an override setting if you have more than one CORE sensor.

Core on Watch OS

As of early 2021, there is now a WatchOS app for the Apple Watch this doesn’t do too much except ‘mirror’ the live temperature reading from the iOS app. There is no true standalone Apple Watch functionality yet.

Core greenTEG Body Temperature Sensor for skin review




CORE Body Temperature Monitor – Quick Start Guide

Here is a link to CORE’s Quick Start Guide video.

CORE Body Temperature Monitor Review – Specifications

CORE claim these specifications

  • Compact: 50 mm x 40 mm x 8.35 mm and weighs 12 grams
  • Highly accurate core body temperature: ±0.21 °C
  • Non-invasive (used on the chest)
  • Not impacted by environment thermal influences
  • Battery life: 6 days continuous transmission time (up to 6 weeks with sleep mode)
  • Rechargeable lithium-polymer battery (via the USB cable supplied)
  • Water-resistant (IPX7)
  • Bluetooth BLE & ANT+ Connectivity
  • APP support: iOS, Android, WatchOS, Wear OS, and Garmin ConnectIQ.

CORE includes:

  • CORE
  • USB charging cable
  • Adhesive patches (1-day usage per patch)
  • Android/iOS App for data downloading

CORE Body Temperature Sensor Review – Problems?

Nope, it’s pretty good really. Sure they are a new and growing company but the product is sound enough to use now.

There are a few mini-glitches here and there in the iOS app and its mildly inconvenient to have to look for and use tHb with a Wahoo as the recording device.

Sometimes the data charts can look a bit messy when you initially wear the device and the algorithms are figuring out what to show for the first few seconds.

My Testing

It’s cold here in the UK right now. I’ve got over 20 hours of CORE data but little of it is even close to closing in on ‘interesting’. Sorry. I did decide to test one moment of craziness in my pain cave. Off went the fans, on went a thick cotton T-shirt and my running hat; obviously the right clothing for an indoor ramp test! Once I reached my FTP point, I stripped off and turned the fans on, I had hoped to trigger a temperature alert but couldn’t get my temperature high enough.

As you can see the data shows up nicely enough in Garmin Connect, although it’s very hard to discern anything interesting from a simple analysis tool like GC.


Perhaps the interesting take-outs from this test data are that 1) skin temperature falls quickly and significantly once I turned the fans on (doh!) and 2) even after completing the test, core temperature kept rising for quite some time, perhaps 10 minutes, and I didn’t expect the latter.

If you try some heat work, the protocol suggested in this image might be a good one to emulate. CORE talk about 80% of FTP as a starting level and 80% of that as the stopping level (with constant HR).



CORE Temperature Sensor Review – Use Cases.

There are going to be a LOT of different use cases for CORE.

In a sports lab setting CORE will readily replace a temperature pill and the alternative more intrusive method (let’s not go there). I once was a guinea pig in a sports lab and ended up in A&E with one of those pills stuck in my throat. So clearly CORE will avoid that and CORE can be re-used, whereas the pills were seen as disposable.

For athletes working in high temperatures then you will want some advance notice that your body is starting to struggle to cope with the heat. CORE is measuring the current CORE temperature but there is a lag before that starts to affect your performance, so if you are alerted you can slow down to mitigate that risk.

Typically the ‘rule of thumb’ for trained athletes is that 38.5ºC is a good threshold to stay below.

I have Raynauds Syndrome which sometimes manifests itself with poor peripheral circulation and this may mean I exhibit non-standard cooling effects. This will be similar in principle to that experienced by some para-athletes and a product such as CORE can help model this for individual athletes.

An athlete such as you might want to try to raise blood plasma volumes by heat training. Normally a minimum of 3-days’ worth of training at times when you get your core temperature up to 38.5 will boost plasma volumes. You would use CORE and a fan to regulate your body’s training temperatures during the workout. Such training would stop prior to a 2-week taper

CORE strikes me as being a more robust sensor for measuring overnight or 24×7 temperatures for researchers investigating issues like jetlag, narcolepsy, insomnia, sleep quality, burnout, Alzheimer’s, Parkinson’s, ovulation status, and others. OK, it IS being used to research those already!

CORE Accessories

The CORE charging cable is OK for me but that wouldn’t be a sufficiently robust charging solution for a team because the magnetic cable comes off relatively easily. Handily, the CORE Team Bundle has a ‘pro’ charger unit. Also available are replacement sticky patches/gaskets, I never tried the ones that came with the CORE.


Core Sensor Review: Cost

Core is £207 direct from here.




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13 thoughts on “CORE Review | pro-Athlete, Skin+Core Temp Sensor by greenTEG

  1. The updated ANT+ profile to include compatibility for this; what do you think are the odds existing Garmin devices will get an update to include this spec? What cutoff do you think will get it?

  2. you tried to run with Core Datafield added on Garmin Connect IQ and used it together wit the new Stryd Running App?

    1. no but i will do.
      data field does have probs when hrm not attached and that bug is being worked on but with hrm paired then even the old 820 didn’t struggle with 2x data fields (humon hex too with pm).

  3. I’ve been playing with my Core unit since it first shipped in October. Overall, I like the additional data set, especially for cross-correlation with others fields.

    So far I’ve only used it with my indoor bike and a Garmin headunit with my other sensors (Moxy + Humon) SmO2, Watts, RPM, HR, ….

    As for the test protocol, it took me ages to ramp up to the right temp (38°C) and even longer to reduce power to keep the HR constant. I suspect my FTP increased since my last test (SUF 4DP + Garmin output) since I couldn’t reach the required stages in the recommended time (50mins to get to 38C, no fans)

    Btw, not sure if you saw Jem Arnold’s testing using the Core, some good insight too:

    1. Thanks for the shout out. Good review here. It’s a very cool device and test protocol for heat accumulation.

      @TK, what was the ambient temp while you were performing the test? What does your core temp usually reach during your typical indoor training (low intensity and high intensity?)

      If you’re a lighter rider that might also tend toward lower core temp and slower heat accumulation, due to lower absolute power output generating less heat, and smaller body size able to shed heat faster.

      1. In my case: 68kg/180cm and I do sweat quite a bit (weight before/after – water intake).
        Ambient temp was approx 19°C when I tested. Nothing extreme IMHO.

  4. I’m keenly interested in this concept however it’s nearly $300 USD. I think I’ll wait until it’s a bit more vetted and down around the price of a quality HRM (ideally included in said HRM)

      1. Really think so? What about adoption that might bring it down to around $200? For example, that’s the price point for the Stryd footpod which seems to provide a lot more functionality than this.

      2. yep, i don’t think it would go any lower than that except at BF, perhaps someone like me might be able to offer a 10% coupon, IDK I’ve asked but they’re not interested.
        it’s a pro product and they need margin if they are a one-trick pony in niche market
        that said, a competitor WOULD spice things up.
        also, it would depend on easily they could scale up volumes if they wanted to more actively target non-pro users
        remember stryd tried the LITE product and backtracked…I made the mistake of thinking that was a good idea too.

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