Comparison

Frontier X vs CORE Thermal Sensor

Price, ratings, monetisation and update history for both apps, side by side — with what reviewers say about each.

Head to head
About

Frontier X

Track your heart health and exercise performance with a smart chest strap monitor. Gain detailed insights into heart rate, rhythms, and training load. Receive personalized feedback and alerts to optimize your workouts and understand your body better.

Highlights
  • Heart Health Monitoring
  • Real-time Heart Rate & HRV
  • Breathing Rate & Strain Tracking
  • Activity Recording (24hrs)
  • Personalized Vibration Alerts
  • AI-enabled Training Insights
  • Metabolic Profile Analytics (Premium)
Features
Read full description

With your Frontier X/X2, track your activity including exercise, rest or sleep to get detailed insights on heart health and exercise performance. This companion app allows you to connect with Frontier X2 - a revolutionary chest strap wearable smart heart monitor and view your recorded data. Trusted by world-class athletes across the globe, the Frontier X2 is a chest-worn Smart Heart Monitor that provides in-depth real-time feedback on your heart health. It can monitor your: - Heart Health - Heart Rate - Heart Rate Variability (HRV) - Breathing Rate - Strain - Rhythms - Training Load - Calories - Stress, and a lot more. • Accurately record your activity like exercise, running, cycling, resting, sleeping, meditation, etc for up to 24hrs with comprehensive heart health insights. • Spot changes in your heart health with Rhythm and Strain. • Train in the right zone without distractions with real-time, personalized, and discreet vibration alerts. • Add health event tags to help you understand how lifestyle choices and behavior affect your health. • Seamlessly integrate with Bluetooth-enabled wearables and third-party devices such as GPS sports watches, bike computers, and more. • AI-enabled algorithms - Receive post-activity training insights, recommendations, and weekly goals. • Frontier X integrates with HealthKit to export your Frontier X activities into the Health app and to read heart rate and biometric data. • IP67 Waterproof up to 1.5 M • Battery: 14+ days of typical use Now get deeper insights and data with Frontier Premium Subscription*: Metabolic Profile Analytics: Track training intensity and the impact of lifestyle changes on metabolic health with key metrics like VO2 Max, VO2 Zones, Oxygen Uptake, and Ventilatory Thresholds (VTs). VO2 Max: Get the most accurate real-time Vo2 Max data. While other wearables estimate using motion and heart rate, our advanced algorithms provides precise Vo2 Max readings outside of a lab, tracking cardiovascular efficiency and endurance potential. Readiness Score: Determine if your body is ready for peak performance or needs recovery. Advanced algorithms use heart rate, heart rate variability (HRV) to guide your daily activities and training. Sleep Stage Analysis: Get a comprehensive understanding of your sleep quality (Webapp). With Frontier's Premium subscription and Metabolic Profile Analysis, tracking your VO₂ max becomes simpler and more precise. *A Paid Frontier Premium subscription is required to access the full feature set . The Premium feature subscription comes with a complimentary 7 days free trial, and continue at a minimal monthly cost starting from USD 14.99, or opt for an annual plan for substantial savings. Please note that prices may fluctuate based on your geographical location, currency, and current exchange rates The Terms of use are available in the app and our website: https://in.fourthfrontier.com/pages/terms-of-use About Fourth Frontier Fourth Frontier is an innovative health-tech company focused on revolutionizing heart health monitoring with its cutting-edge wearable technology. We are the World’s First Smart Heart Monitor. With over 5 billion heartbeats recorded from 120,000+ users across 50+ countries, we are empowering users to understand and manage their heart health in real-time. These features make the Frontier App a comprehensive tool for heart health management and fitness improvement. Download the app today and access the most accurate heart health data available. Apps available for iPhone and Apple Watch.

About

CORE Thermal Sensor

This app continuously monitors your core body temperature and thermal strain, providing critical data for heat training and optimal race performance. It helps athletes of all levels improve their training and achieve better results.

Highlights
  • Continuous core body temperature monitoring
  • Real-time Heat Strain Index
  • Heat Zones for training and racing
  • Heat Training Load and Adaptation Score
  • Passive heat training tracking
  • Data trends and historical analysis
  • Connectivity with sports devices
Features
Read full description

The CORE Thermal Sensor accurately measures your core body temperature and thermal strain on your body – continuously and non-invasively. Thermal data and insights are critical for facilitating safe and effective heat training and for performing optimally on race day. Designed for athletes at all levels, CORE will help to improve your training and performance in your personal adventures or races. IMPORTANT: The CORE app is designed to work with the CORE device which you can order at www.corebodytemp.com Here's how it works: • Set up your CORE sensor: connect your heart rate monitor and sports devices for optimal sensor use. • Measure your thermal vitals during training: mount the newly designed clip on your heart rate strap and snap in the CORE sensor. Shake the sensor to wake it up, wear it and track your thermal data. • Core body temperature: the interior temperature deep in your body, including organs and other tissues. A critical measure during sports, it can reach up to 40°C (104°F) during vigorous activity in hot environments. Be aware that hotter is not better – cooler is faster. • Heat Strain Index: A combination of your core body temperature and skin temperature representing the thermal strain on your body. The real-time feedback on how hard your body is working to stay cool, delivering a value from 0 (no heat strain) to around 10 (extremely high heat strain). • Heat Zones: Your Heat Strain Index divided into easy-to-use zones. Heat Zone 3 will likely lead to a performance loss, BUT it is the needed stimuli to create adaptations in your body. During heat training, strive for time in heat zone 3. During racing, stay cool and prevent a performance loss by staying in heat zone 1 or 2. • Heat Training Load: a cumulative daily metric of the heat strain on your body. A daily value of 10 out of 10 indicates ideal contribution to heat adaptations. More is not always better! • Heat Adaptation Score: Track your heat adaptations over time with effective heat training. Get a heat champion to perform best in the heat. Long-term heat training will most likely lead to improvements also in cool conditions. • Add your passive heat training: Supplementing your active heat training or general training with passive heat exposure in a sauna or hot bath. You can track your sessions in the app manually, contributing to your heat adaptation score. NOTE: do NOT take your CORE sensor into the sauna or hot environments. What else you can do in the CORE app: • Dig into the details: See a breakdown of your thermal data, and even see trends across days, weeks and months. • Share your CORE metrics with your friends through the social sharing feature, earning more kudos and likes • Connect your connectivity accounts (e.g. Garmin) to directly synchronize your data after the training. • Update your sensor to the latest firmware ensuring having the best sensor functionality. Note: CORE provides products and services designed for general fitness and training purposes. For accurate measurement readings during sports, a connection to a heart rate monitor is necessary. CORE products and services are not medical devices, not intended to treat or diagnose any disease, and should not be used as a substitute for professional medical advice, diagnosis or treatment. All content available through CORE products and services is for general informational purposes only.

Screenshots

Frontier X4 screens
CORE Thermal Sensor4 screens

Verdict

The call

The clearest difference is review sentiment: Frontier X at 82% against CORE Thermal Sensor's 16%. Frontier X also leads on rating (4.6 vs 2.5) and update cadence (every 3 weeks vs every 2 months). CORE Thermal Sensor's advantage is in-app purchases (none vs 2). On price, ads, device support and iOS requirement there is nothing between them.

Scored on Price · Rating · Positive reviews · Number of ratings · Update frequency · Ads · In-app purchases · Monetization · Best chart rank · Devices · Requires iOS

CostPrice · In-app purchases · Ads · Monetization

Both are free to download. Frontier X sells 2 in-app purchases, starting at $14.99 per month. CORE Thermal Sensor asks for nothing beyond the download.

ReceptionRating · Positive reviews · Number of ratings

Frontier X holds the better App Store score, 4.6 against 2.5. That said, the two scores are not equally well evidenced: Frontier X has 317 ratings behind it against 35, so its average is the more settled of the two. Written reviews point the same way: 82% of Frontier X's written reviews are positive against 16% of CORE Thermal Sensor's.

UpkeepUpdate frequency

Frontier X ships an update every 3 weeks, CORE Thermal Sensor every 2 months. Both last shipped on September 23, 2026.

Scorecard6 real differences · 4 level
Frontier X versus CORE Thermal Sensor: the parameters behind the verdict, then further details
ParameterFrontier XCORE Thermal Sensor
PriceFreeFree
Rating4.6 (317 ratings) — better2.5 (35 ratings)
Positive reviews81.8% of reviews — better15.6% of reviews
Number of ratings317 — better35
Update frequencyEvery 3 weeks — betterEvery 2 months
AdsNoNo
In-app purchasesYesNo — better
MonetizationFree with in-app purchasesFree — better
DevicesiPhone, Apple WatchiPhone, iPad, iPod — better
Requires iOS16.015.1 — better
Further details — not scored
Size571 MB55 MB
Age rating4+4+
DeveloperFourthfrontiergreenteg AG

Customer experience

Frontier X

All ratings317 ratings
Positive90.9%
Neutral1.3%
Negative7.9%
Written reviews137 reviews
Positive81.8%
Neutral1.5%
Negative16.8%

CORE Thermal Sensor

All ratings35 ratings
Positive22.9%
Neutral20.0%
Negative57.1%
Written reviews32 reviews
Positive15.6%
Neutral25.0%
Negative59.4%

Bugs and requests

Frontier X

Reported bugs

4 issues
  • ECG stopped working
  • Inaccurate breathing rate and other metrics
  • Inability to edit activity details for indoor workouts
  • Syncing issues with Garmin devices after firmware updates

Requested features

6 requests
  • Add interval markers
  • Improve integration with Apple Fitness/Fitness+
  • Add support for ANT+
  • Improve compatibility with other fitness apps and devices
  • Add more customization options for workouts
Show 1 more
  • Improve data visualization and analysis tools

CORE Thermal Sensor

Not enough reviews yet to summarise bugs or requests.

In-app purchases

2 purchases

Frontier X

Subscriptions2
  • Monthly7 Days trial$14.991 Month
  • Yearly7 Days trial$119.991 Year
None

CORE Thermal Sensor

No in-app purchases

Questions

Is Frontier X free?
Frontier X is free to download, with in-app purchases available.
Is CORE Thermal Sensor free?
CORE Thermal Sensor is free to download, with no in-app purchases.
Which has better reviews, Frontier X or CORE Thermal Sensor?
Frontier X is rated higher. Frontier X averages 4.6 out of 5 from 317 ratings, while CORE Thermal Sensor averages 2.5 from 35 ratings.
Do Frontier X or CORE Thermal Sensor have ads?
Neither Frontier X nor CORE Thermal Sensor shows ads.
Which is updated more often, Frontier X or CORE Thermal Sensor?
Frontier X ships an update every 3 weeks, and CORE Thermal Sensor every 2 months. Most recently, Frontier X was updated on September 23, 2026 and CORE Thermal Sensor on September 23, 2026.

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