Reviewer spotted wearing 5 optical bicep bands – Garmin CIRQA?

The latest pictures show a reviewer wearing 5 optical HR bands. Surely, one must be Garmin CIRQA? If not, then maybe one is the speculative Coros Whoop-Wannabe for 2026? Or perhaps a modified, Whoop-case-busting Polar upgrade to the Loop?

Proof, if it were ever needed, that you can’t always believe what you think you see.

It made me wonder how close sensors can be placed.

Some Science

I first anecdotally heard about the potential for intra-device interference from sensor‑maker Valencell years ago, but what’s the exact safe distance?

Lab scientists care about sensor spacing for optical PPG accuracy. However, most athletes will not stack multiple devices on one muscle the way I did, so dedicated research on inter‑device interference is rare and relatively unimportant. It would matter for lab studies that require multiple sensors on the same limb (though chest straps remain the smarter reference; I use them in my tests).

The main published work I found was Akinlabi, A. (2023). “Effects of Wavelength and Sensor Layout on the Quality of Reflective Photoplethysmogram.” Tampere University. This small-scale Master’s Thesis focuses on distances within a single sensor array (LED–photodiode spacing), not on the spacing between separate devices.

For my use case, a reasonable inference from Akinlabi’s wavelength‑ and spacing‑dependent results, combined with how strongly green light is lost as it travels though tissue, is that once two sensors are separated by around 5 cm on the same limb, any direct optical contribution from one into the other will be far below the second sensor’s own signal‑to‑noise ratio and effectively negligible. That 5 cm figure is therefore an informed interpretation for multi‑device setups, not a distance that Akinlabi directly tested.

Spacing Within a Single Array

I have added a few other sources on related issues further below. For example, Morillo et al. show that distance within a PPG configuration matters, reporting lower variability when detector placements are around 9–12 mm from the source rather than 6 mm; that is intra‑sensor spacing, but it illustrates how sensitive things are to a few millimetres’ change.

Conclusion

Definitely don’t wear more than two sensors on one arm.

1. Akinlabi, A. (2024)
   Effects of Wavelength and Sensor Layout on the Quality of Reflective Photoplethysmogram (Master’s thesis, Tampere University). The thesis empirically evaluates how sensor layout and source–detector configuration influence reflective PPG signal quality, including a discussion of spacing effects between LEDs and photodiodes. (trepo.tuni.fi)
2. Solé Morillo, Á., Cause, J. L., De Pauw, K., da Silva, B., & Stiens, J. (2025). Exploring near- and far-field effects in photoplethysmography signals across different source–detector distances. Sensors, 25(1), 99. https://doi.org/10.3390/s25010099 (MDPI)
3. Reiser, M., Mueller, T., Breidenassel, A., & Amft, O. (2025). Source-detector geometry analysis of reflective PPG by measurements and simulations. IEEE Open Journal of Engineering in Medicine and Biology, 6, 400–406. https://doi.org/10.1109/OJEMB.2025.3546771 (PMC)
4. Charlton, P. H., Marozas, V., et al. (2025). Determinants of photoplethysmography signal quality at the wrist. PLOS Digital Health, 4(6), e0000585. (PMC)

Last Updated on 1 February 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.