Heat training has become de rigueur among athletes the world over and the evidence suggests there are significant performance gains to be made by incorporating it into your workout regime.

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The first-generation Core sensor has been around for four years now but Greentag AG has finally dropped the covers off its latest incarnation by refining the recipe and sensor blueprint for a more immersive and accurate experience. 

What's new with Core 2?

Core 2 heat sensor, by Aaron Borrill

First off, the unit is 48% smaller and 30% lighter than the model it replaces, so you barely notice it when fitted to your heart rate strap. There’s also a revised modular attachment housing for easy removal for charging – the housing is malleable and remains attached to the heart rate strap. (For those who don't have a heart rate monitor, the website still offers medical-grade adhesive patches to secure it to your skin). There’s also a new red LED battery indicator which flashes when the unit needs to be charged. 

While a new magnetic USB-C charging cable is included in the box, the original Core 1 charger is still compatible.

Like before, the Core app is available on iOS and Android platforms. The sensor is compatible with most smartwatches and cycling computers from Garmin, Coros, Suunto, Wahoo and Hammerhead. The Core 2 also has an expanded ecosystem and can be paired with the GarminConnectIQ app to show metrics such as Heat Zone, Time in Zone and Heat Strain Index for easy-to-digest and understandable data. More app integrations are rolling out in the weeks ahead including Zwift, TrainingPeaks and other third-party apps.

For better accuracy in terms of the Heat Adaption Score, there’s a Passive Heat Training facility allowing users to manually input sauna sessions to plan daily heat strain. The experts at Core say optimal heat training involves 2–3 sessions per week, with 45–60 minutes per session in the heat training zone. Sequential days with a high Heat Training Load will increase your Heat Adaptation Score.

Core 2 heat sensor, by Aaron Borrill

These new metrics and training zones have been shown to improve VO2 max (4-6% in sub-elite athletes), improve time trialling and increase haemoglobin mass by 2.5% with sustained heat acclimation.

To ensure accuracy of the highest order the Core 2 uses Swiss Sensors to ensure real-time core temperature monitoring – the unit can record both skin and core temperature.

Trade-in scheme

Owing to the cost of living crisis and global environmental issues, Greentag AG is offering a trade-up scheme for existing Core users, to trade in their Core 1 device and receive 30% off a Core 2 upgrade (available from March 25 to June 30, 2025).

Pricing and tech specs

Core 2 heat sensor, by Aaron Borrill

The Core 2 sensor will retail for £264.95 / €314.95 / US$294.95 and orders begin shipping the week of April 14th, 2025.  Accessories such as the Core Heat Training Suit can be purchased separately.

We've been using the Core 2 sensor for a week already and will be publishing a detailed review in due course – make sure you check back in a few weeks to read all about it.

• Dimensions: 41.9 x 29.4 x 7.1mm (sensor only), 45.1 x 32.6 x 9.6mm (with housing)
• Weight: 8.6g (sensor), 11.4g (with housing)
• Battery: Up to 6 days (active), 30 days (standby)
• Charging: USB-C magnetic adapter cable
• Connectivity: BLE & ANT+ (2.4 GHz band)
• Waterproof: IPX7 (up to 1.5m)
• ​Accuracy: Mean difference range of -0.01°C to +0.23°C
   
• www.corebodytemp.com

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