

CORE 2
Internal body temperature measurement
CORE is a cutting-edge body temperature monitoring device that helps athletes improve performance through efficient heat adaptation. It tracks core temperature in real time and calculates heat strain, allowing for smarter pacing during training and races. The app records time spent in heat zones and evaluates heat load to optimize the training process.
↓ 5%
possible performance loss with each 1°C increase in core temperature
↑ 2.5%
increase in hemoglobin mass after long-term heat training shown in research


Advanced Metric Tracking
Train and race based on data
Unique and scientifically-backed metrics that elevate your heat preparation for peak performance on race day.
Heat Strain Index. Describes the physiological processes your body uses to cool down. The harder your body has to work to cool itself, the greater the strain and the more performance is impacted. CORE 2 quantifies this strain in real time through an algorithmic combination of core and skin temperatures.
Heat Zones. Your heat strain index falls into one of 4 zones. The training zone (Zone 3) triggers physiological adaptations that enhance performance. Time spent in each zone is recorded in the CORE app.
Heat Training Load. Your daily heat training load (scale 0–10) reflects time spent in the training zone (Zone 3). Optimal heat training includes 2–3 sessions per week, each 45–60 minutes. Multiple high-load days increase your heat adaptation score.
Heat Adaptation Score. The human body can adapt remarkably well to heat. This score uses a scientifically validated algorithm to calculate your heat adaptation level from 0 to 100%. Use heat zones to achieve high daily heat loads, which gradually improve this score.
Core and Skin Temperatures. Core temperature reflects the heat around internal organs. It rises during physical activity, and if it gets too high, performance drops. Skin temperature fluctuates more with the environment. Both are used to calculate the heat strain index.
Cooling Strategy
Control your body temperature
The CORE sensor helps you understand thermoregulation trends so you can act early and efficiently – by hydrating or pouring water over your head, for example. It connects with GPS watches or bike computers for real-time core temperature monitoring.
Real-time feedback. See your core temperature live on your watch or bike computer and make informed cooling decisions.
Compatibility. Easily pairs with COROS, Suunto, Garmin, Wahoo, Apple Watch, Android, Fulgaz, Hammerhead, TrainingPeaks, and more.

Why Shop at ralpu e-shop
Always in Stock
Only items that are physically in stock are sold. Your order is shipped immediately. Package is usually delivered within 1 - 2 business days. No tricks.
Guaranteed Satisfaction
Products come with 24-month warranty. In case of questions, you can expect prompt and helpful response. COROS GPS watch manuals are translated to Slovak.
Authorized Dealer
ralpu e-shop is an authorized dealer of CORE brand in Europe with long-standing experience and appreciated by thousands of customers. You can rely on us.
Frequently Asked Questions
Here are the answers
Why is core body temperature important for performance?
Muscles generate heat when working. If we produce enough heat, core temperature rises. The body tries to cool itself by sending blood to the skin, where sweat evaporates. This diverts blood away from muscles and reduces performance. You can minimize this by (1) using real-time core temperature data for strategic decisions during training and racing, and (2) training in heat to adapt to higher internal temperatures. In one study, cyclists improved their time trial performance by 8% after just 10 days of heat training.
What data does CORE 2 measure and display?
CORE 2 measures both core and skin temperature. These values are shown live in the app and on compatible sports devices (e.g., GPS watches or bike computers). The app and some Garmin devices also display real-time heat strain index, indicating how much thermal stress your body is under.
How should I use CORE 2 during training or races?
During heat training, use CORE 2 data to keep your core temperature within the heat training zone. In races, the data can help you decide when to cool down or reduce effort to avoid overheating.
How much heat training is needed to see results?
Max benefits are seen after 10–12 sessions over 2–6 weeks. Most athletes improve after 4–5 sessions. Maintaining benefits only requires 2–3 sessions weekly. Each session should include 45–60 minutes of continuous effort in the heat training zone. Even less frequent sessions have shown performance benefits.
I race only in cool weather. Why add heat training?
Heat training improves performance at higher core temperatures and increases blood plasma and hemoglobin volume, boosting performance in both cold and hot conditions.
What is the science behind heat training benefits?
The impact of heat on performance is well studied. Heat training improves the body’s ability to handle high temperatures, cool more efficiently, and perform in all environments. It increases plasma and hemoglobin volume, sweat rate, and earlier onset of sweating. You can find supporting research here.
Is the CORE 2 sensor accurate? How is it tested?
CORE 2 measures heat transfer between body and environment. An AI-based algorithm calculates core temperature with medical-grade accuracy. Extensive testing has confirmed accuracy compared to invasive methods like ingestible pills. Athletes can trust this non-invasive wearable to reliably understand their core body state. More accuracy info here.
Is CORE 2 compatible with my watch, bike computer, or app?
The CORE 2 app is available on iOS and Android. The sensor works with COROS (software Jan 2022+), most Garmin, Suunto, Wahoo, Hammerhead devices. Apple and WearOS support is improving. Training platforms like Today’s Plan, Intervals.icu, Golden Cheetah, and premium TrainingPeaks are compatible. Full compatibility list here.
Do I need a heart rate monitor (chest strap) to use CORE 2?
Pairing CORE 2 with a chest strap HR monitor is strongly recommended for the most accurate data during sports. Heart rate helps translate heat flow into accurate core temperature readings. Outside of workouts, temperature data is accurate with or without it. Consider using CORE 2 with a COROS Heart Rate Monitor.


Box Contents
What's in the Box
-
CORE 2 Heat Sensor
-
CORE 2 HRM Strap Clip
-
Magnetic USB-C charging cable
Technical Specifications
Product Parameters
Dimensions & Weight | |
Physical dimensions | 41.9 mm height × 29.4 mm width × 7.1 mm depth (without mounting mechanism) 45.1 mm height × 32.6 mm width × 9.6 mm depth (with mounting mechanism) |
Weight | 8.6 g (without mounting mechanism) 11.4 g (with mounting mechanism) |
Wearing Method | |
Description | Non-invasive (i.e. no piercing of the skin), worn on the chest (ideal) or on the upper arm |
Battery | |
Battery life during activity | 6 days of continuous monitoring and data transmission to watch or bike computer |
Battery life in standby mode | Up to 30 days in Sleep Mode |
Battery type | Rechargeable lithium-polymer battery |
Charging method | Proprietary magnetic connector on sensor side, USB-C cable on power supply side (included) |
Measurement Accuracy | |
Details | Research-validated measurement accuracy Average measurement deviation: -0.01°C to 0.23°C |
Additional info | Measurements are unaffected by external environmental heat conditions |
Connectivity | |
Supported wireless protocols | Bluetooth Low Energy (BLE), ANT+ (2.4 GHz) |
Device pairing | CORE iOS and Android app, devices from COROS, Suunto, Garmin (ConnectIQ watches and bike computers), Wahoo, Apple Watch (WatchOS), Android (Wear OS), Fulgaz, Hammerhead, TrainingPeaks, etc. Full and updated list of compatible devices available here. |
Durability | |
Water resistance | IPX7 standard – immersion up to 1.5 meters |
AI-optimized Markdown version for CORE 2 - core body temperature monitoring sensor
Download AI Markdown
(Markdown/AI Version)