The Core 2 Thermal Sensor Is 20% for Cyber Monday

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Black Friday sales officially start Friday, November 28, and run through Cyber Monday, December 1, and Lifehacker is sharing the best sales based on product reviews, comparisons, and price-tracking tools before it's over.

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Normally $295, the Core 2 Thermal Sensor is currently on sale for $236-a 20% discount for Cyber Monday. And here's the smart play: buying it now means you'll be ready to get ahead of the heat when spring training season rolls around.

Core 2 Thermal Sensor $294.95 at CORE Get Deal Get Deal $294.95 at CORE What the Core 2 does

The Core 2 is a small plastic sensor that attaches to your heart rate monitor chest strap and tracks your body temperature during workouts. It's designed to help you understand how heat is affecting your performance, and guide you through heat-training protocols so you can adapt faster and more efficiently.

My colleague Beth Skwarecki reviewed the Core 2 and found it a little fussy to set up, but easy to use and understand once you're up and running. What really impressed her was the big-picture view it provides: tracking how your body adapts to heat over time.

Train hot, race cool

The data from the Core 2 serves two main purposes. First, it can guide your heat acclimation training-helping you adapt to hot conditions more strategically. Second, you can use it during races to monitor your core temperature and avoid overheating when it counts.

As Beth points out, there's a legitimate debate about whether heat training makes sense for every athlete. You could argue that most runners would benefit more from longer or faster runs rather than adding heat stress to their training. But if you are training in the heat-whether because you live somewhere hot, you're preparing for a warm-weather race, or you're intentionally pursuing heat adaptation-the Core 2 seems to be an incredibly useful tool.

Worth it for the right runner

At nearly $300, this isn't an impulse purchase. But at $236, it's more accessible for serious athletes who want to take their heat training to the next level. Getting it now during Cyber Monday means you'll have months to familiarize yourself with the device before temperatures climb in spring and summer. By the time race season heats up, you'll already know exactly how your body responds to thermal stress-and how to manage it.

How long do Black Friday deals really last?

Black Friday sales officially begin Friday, November 28, 2025, and run throughout Cyber Week," the five-day period that runs from Thanksgiving through Cyber Monday, December 1, 2025. But Black Friday and Cyber Monday dates have expanded as retailers compete for customers. You can get the same Black Friday sales early, and we expect sales to wind down by December 3, 2025.

Are Black Friday deals worth it?

In short, yes, Black Friday still offers discounts that can be rare throughout the rest of the year. If there's something you want to buy, or you're shopping for gifts, it's a good time to look for discounts on what you need, especially tech sales, home improvement supplies, and fitness tech. Of course, if you need to save money, the best way to save is to not buy anything.

Are Cyber Monday deals better than Black Friday?

Black Friday used to be bigger for major retailers and more expensive tech and appliances, while Cyber Monday was for cheaper tech and gave smaller businesses a chance to compete online. Nowadays, though, distinction is almost meaningless. Every major retailer will offer sales on both days, and the smart move is to know what you want, use price trackers or refer to guides like our live blog that use price trackers for you, and don't stress over finding the perfect timing.

Our Best Editor-Vetted Cyber Monday Deals Right Now Apple AirPods Pro 3 Noise Cancelling Heart Rate Wireless Earbuds - $219.99 (List Price $249.00) Apple iPad Air 11" M3 128GB WiFi Tablet (Space Gray) - $449.99 (List Price $599.00) Dell 14 Premium DA14250 (Intel Core Ultra 7 255H, 512GB SSD, 16GB RAM, 2K Display) - $999.99 (List Price $1,549.99) Sony WH-1000XM5 - $248.00 (List Price $399.99) Blink Outdoor 4 1080p Wireless Security Camera (5-Pack) - $159.99 (List Price $399.99) Amazon Fire TV Stick 4K Plus - $24.99 (List Price $49.99) Shark AI Ultra Matrix Clean Mapping Voice Control Robot Vacuum with XL Self-Empty Base - $249.99 (List Price $599.00) Apple Watch Series 11 (GPS, 42mm, S/M Black Sport Band) - $329.00 (List Price $399.00) WD 6TB My Passport USB 3.0 Portable External Hard Drive - $136.45 (List Price $179.99) Samsung Galaxy Tab A9+ 10.9" 64GB Wi-Fi Tablet (Graphite) - $139.99 (List Price $219.99) Deals are selected by our commerce team