Garmin CIRQA – First Test Accuracy Fail – Open Water Swim

A beautifully warm evening cried out for open-water swimming and my first test of CIRQA. I was wearing it on the wrist and expected the worst. I wasn’t disappointed.

Test conditions

There were two 15-minute efforts at a bit below threshold recorded by Apple Watch Ultra 3 (left wrist), Garmin CIRQA (right wrist, configured as such), Polar Sense (right biceps), WHOOP MG (left biceps) and HRM 600.

Problems

I had two problems. Firstly, the HRM 600 didn’t record the session even though I specifically started and remembered stopping it at the end. Whether Connect was getting confused between two caching devices simultaneously recording a workout, I don’t know. Maybe I made a mistake.

The second problem was that I wasn’t quite sure if CIRQA was recording or not. It was very hot and bright, and I couldn’t see the tiny light. After the first 15-minute effort, I stopped CIRQA to check the vibration was signalling the end of a saved workout (it was). So I started a second workout. Consequently, the CIRQA results are split into two files as you can see from the test results. That makes zero difference, as the results were awful.

Test interpretation

In this open-water swim test, CIRQA under-read heart rate substantially compared with the competing devices. Polar Sense (121.89 bpm), WHOOP (119.42 bpm) and Apple Watch Ultra 3 (113.87 bpm) agreed closely with one another (excellent bias and tight limits of agreement), whereas the two split CIRQA files averaged only 99.45 bpm and 96.77 bpm. Pairwise comparisons showed large positive biases of roughly +20 to +30 bpm for WHOOP and Polar versus both CIRQA segments (rated Poor), confirming a clear systematic under-reading by CIRQA relative to the other devices on this swim.

Take out

CIRQA was worn correctly. I even suffered wearing a wetsuit to ensure it was firmly held in place during the swim.

I was wholly unsurprised that I got bad heart rate tracks on the wrist from a prior gen sensor (Elevate 4.1). I am going to put myself through misery over multiple tests with CIRQA on the wrist. I fully expect it to be wrong much of the time. I hope I’m wrong. I want to say that I’m pretty sure it will be accurate on the biceps, as most devices are, but you’ll likely be risking your chances with it on the wrist. I’m pulling one for the team here and getting the bad results out of the way.

Quick answers

Is the Garmin CIRQA accurate for heart rate on the wrist?
In this open-water swim test, the wrist-worn CIRQA under-read heart rate by roughly 20 to 30 bpm against Polar Sense, WHOOP MG and Apple Watch Ultra 3. Wrist optical sensors struggle in open water, and this early result is consistent with that pattern. Further testing will follow.

Which heart rate sensor does the Garmin CIRQA use?
The CIRQA uses Garmin’s Gen 4 optical sensor (Elevate) with skin temperature added, which this site labels 4.1. It reads heart rate, HRV, SpO2, respiration and skin temperature.

Is the CIRQA more accurate on the upper arm than the wrist?
Optical sensors are generally more accurate on the upper arm than the wrist because the arm moves less and offers steadier blood flow. The CIRQA supports upper arm wear with a dedicated band, and arm placement is the more reliable option for heart rate during hard efforts.

Last Updated on 30 July 2026 by the5krunner

the5krunner

tfk is the founder and author of the5krunner, an independent endurance sports technology publication. With 20 years of hands-on testing of GPS watches and wearables, and competing in triathlons at an international age-group level, tfk provides in-depth expert analysis of fitness technology for serious athletes and endurance sport competitors. ID