BUG: OHR sensor crashes with non-ideal skin conditions (hair, dirt, small tattoo marks)

Manuel Extreme

[Suunto Vertical 2 - 2.53.43] OHR sensor crashes with non-ideal skin conditions (hair, dirt, small tattoo marks)

Description
The optical heart rate (OHR) sensor crashes when the skin is not in optimal condition. Presence of hair, dirt, or even very small marks (e.g. ~1 mm tattoo or ink mark) over the sensor LEDs causes the sensor to stop working. This results in long periods (hours) without heart rate data.

The issue was observed immediately on first use after release. The device was sent to support and replaced, but the problem persisted identically on the new unit. Firmware updates did not resolve the issue. The problem does not occur on Suunto Vertical 1 or other sport watches.

Reproducible steps (if applicable)

Wear the watch on clean skin
Create a small mark over the OHR sensor area (e.g. with a pen or presence of hair/dirt)
Keep the watch at rest
Observe OHR behavior

Expected result
The OHR sensor should continue providing heart rate readings, even if signal quality is reduced. It should not shut down or stop recording data.

Actual result
The OHR sensor stops working completely, producing no heart rate data for extended periods (hours). The sensor resumes working only after removing the watch from the skin and placing it back again.

Context (if not reproducible)
Occurs at rest. The issue is consistently reproducible when skin conditions are not optimal. Requires perfectly clean skin (e.g. right wrist) to avoid the problem.

Additional details

Suunto App version: iOS 3.9.0 (22101)
SuuntoPlus Apps: none
Watch face: N/A
Activity type: none (rest)
Frequency: always

Attachments

Activity link: N/A
FIT file: N/A
GPX file: N/A
Media: N/A

Logs
Logs N/A

Notes
Issue reported multiple times and persists across device replacement and firmware updates.

BrunoH

@Manuel-Extreme

I think you are jumping to conclusions. What makes you think the sensor crashes? Inability to produce reliable measurements because of non ideal conditions is not a crash.

It’s been a long time subject of debate that OHR works better for some people and worse for some others, and it’s been a tough cookie to swallow for certain persons. They see the price tag and demand that OHR must work flawlessly in all conditions. Different types of skin and the amount of hair are definitely part of the equation, also the blood veins differ from person to person. Some claim that Apple sensor is better, some have esperienced that they are all equally unreliable. I think that having seen this same discussion going in circles for several years it is safe to say that with today’s technology you can’t get a fool proof method.

It is also common sense that it will fail if you block the path of light with tattoos, dirt or markers.

I know the pain, my Vertical 1 is unreliable in my acitivities, mostly cycling and hiking. I sweat a lot and particles of dirt and dust get under the watch, just as it should with an adventure watch like this. I often get better results by turning my watch to the inside of my wrist. Or I use my heart belt if I want precise measurements.

Basically it seems that your bug report demands that the sensor’s light must penetrate any foreign matter that might get between the skin and the sensor. Does it sound reasonable?

Manuel Extreme

@BrunoH sensor crash:

Manuel Extreme

I have been studying, testing, and comparing optical sensors for 10 years. I know very well how they work and I understand the difference between a malfunction and a reading error.

I did not report a reading error. I did not report suboptimal conditions. I did not report inaccurate heart rate readings.

This report is about a crash/shutdown at rest without any clear reason. The sensor suddenly turns off without warning, even though the conditions in which it was previously working have not changed.

I have used the following wrist-based optical sensors over the past 15 years:

Garmin Fenix 3 HR
Garmin Fenix 5X
Garmin Fenix 6X
Suunto Vertical 1 steel no solar
Suunto Vertical 1 titanium solar
second Suunto Vertical 1 titanium solar
Garmin Fenix 7X
Suunto Vertical 2
Garmin Fenix 8
Garmin Vivosmart 4
Garmin Vivosmart 5
Whoop 4
Whoop 5

(Basically the entire Elevate lineup)

This shutdown issue occurs only with the Vertical 2.

BrunoH

@Manuel-Extreme

You sure made a convincing point! I am starting to believe you.

Have you sent the logs to Suunto and notified the contact persons here in the Forum?

Egika

hm.
There are two things I can add:

my arm has a lof of hair. The sensor has never stopped working for me. So the issue you observed is maybe not just caused by non-ideal skin conditions.
The watch has some off-wrist detection. I am not sure what triggers it, but if you put the watch on a non-reflective surface, it will stop the HR reading.

Putting 1 and 2 together: maybe for you the off-wrist detection became active as the sensor sat on a very dark part of the skin. Still a fine line should not be sufficient…

What do you think?

Manuel Extreme

@Egika It may well be a contact-based detection system, but it behaves oddly.
It works for hours, then suddenly turns off and stays off until I physically remove the watch from my wrist.
My guess is that, while trying to correct a reading error, the sensor logic may crash and fail to recover. Possibly some kind of overflow or state-handling bug. It does not seem to reactivate until the watch changes state from on-wrist to off-wrist and back again.

Egika

@Manuel-Extreme off wrist detection is not contact based, but somehow optical.
From here on I have no more ideas, sorry.