If you’ve already got a smartwatch you like, here’s what I’d get in the Prime Day sales — the Polar H10, the ‘gold standard’ electrical heart rate monitor

Every smartwatch and fitness tracker comes with heart rate tracking, but they’re not all accurate, so we test them against a Polar H10 chest-mounted heart rate monitor. The Polar H10 is used by athletes all around the world, and can be linked to a smartwatch to provide incredibly accurate metrics using its electrode system. Now it’s on offer in the Amazon Prime Day sales, and if you care about fitness tracking, you should probably get one.

• Browse the full Amazon Prime Day sale

The Polar H10 works with a strap that goes around your ribcage underneath your heart, and connects the device to the electrodes running along the underside of your band. These electrodes monitor the electricity generated by your heart when it expands and contracts.

This is very different to (and more reliable than) the way smartwatches and the best fitness trackers measure your heart rate on your wrist. These devices use LED-based optical heart rate monitors, shining lights through your skin to measure your heart rate by detecting the changes in your blood flow. Electrical heart rate monitors are simply more accurate.

Fortunately, most smartwatches allow you to pair up a heart rate monitor like the Polar H10 via Bluetooth or ANT+ networks, so you can incorporate the more accurate data from the chest strap into your recovery and health metrics. Most heart rate monitor users tend to wear them only during workouts for the more accurate data, then rely on other fitness trackers for a general 24/7 overview. So, if you care about your fitness tracking and you already have a smartwatch you like, the Polar H10 should be your next purchase.

Right now, you can get the Polar H10 heart rate monitor (with black M-XXL strap) for $76.99 (was $104.95) at Amazon US. Those who need a small strap will need to pay a little extra — it’s in XS-S for $89.21 (was $104.95) so you still get a little discount.

In the UK, you can get the Polar H10 with XS-S strap for £59.92 (was £70.49) and the Polar H10 with M-XXL strap for £65.99 (was £86.70).

There are other heart rate monitor designs out there, such as the more expensive Garmin HRM 600 that interfaces with the Garmin Connect app in a less roundabout way than Polar.

Armbands exist too, if you prefer those to chest straps, although these tend to use optical technology rather than electrodes. The Polar Verity Sense and Coros Heart Rate Monitor are armbands, and during testing they’ve proved nearly as accurate as the H10 due to the placement on the arm being better than the wrist. Check out the best deals on those products below.

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