Tattoos ...have i messed up?

Not necessarily. Wrist HR is problematic at the best of times for anything other than low intensity activities. You may or may not find it works for you as the results are good for some. The tattoos are likely to affect the results but you really won't know until you try. If you do plan to be actively active then a chest strap would be the way forward to ensure more reliable results.

To be fair, it's not just Garmin wrist heart rate that has the problem. It's all of them using the same system to a greater or lesser degree. The sensor is trying to detect a colour change as blood pumps through the blood vessels under the skin as function of reflected light from the leds. I'm guessing most people would not be checking the finer points of how pulse is detected too, so you are not alone in being caught out. Bear in mind that people with darker skin and lots of body hair also have problems.

Not heard of the scotch tape over the sensor before. But, yes you'll have to try and see how the results stack up.

spamdog There is a potential for you to have inaccurate readings with optical heart rate due to tattoos, but this certainly isn't a guarantee. We would advise you to see what your results are once your devices arrive as everyone's experience will be different. Also, as philipshambrook mentioned, using a heart rate strap will provide the most accurate readings during your activities, although this does not address 24X7 heart rate reading.

If you find that you have any additional questions once your devices arrive, please reach out to us directly through support.garmin.com as we will gladly work with you to answer any questions or resolve any issues you may have.

P.S. For what it's worth, a neighbor of mine in the office has two full sleeves and is able to use our optical heart rate sensors without issue.

Only the little green light needs to be over skin without a tattoo, and you don't need to wear it like a fashion watch - it works on almost any skin even if it is much higher or lower on your arm or facing the wrong way. If your wife really wants a fitness tracker, all the optical sensors will have the same problem, so you didn't go wrong picking a 645. But you might need chest straps.

spamdog as some have alluded, if you have more than a casual interest in your heart rate and using it for training, I suggest getting a chest strap. This would apply to anyone regardless of tattoos.

So as a person that used OHRM on wrist and forearm and Bicep before Tattoos and after Tattoos; There are a few things to take into account.

All OHRM use the same tech (LED's) but how they read the data, what kind of configuration they employ, if they use a different color LED to diffuse light are different and will play a factor. Wrist-Based tends to be underwhelming with reporting when you're dealing with higher HR's. The forearm/Bicep units tend to be much more accurate (but in my opinion slower in the delivery of data than a chest strap). With that being said; if you're dealing with tats with a Wrist-based OHRM's, there isn't more I can say. The measurements are not steady already, to begin with.

Now, with the Forearm/bicep units, it depends. There have been studies on darker skin not being conducive to LED's reading blood flow under the skin, but and this how I understood it, Ink from a tattoo (fully set) resides in the Dermis (2nd layer) which is rich in the blood vessels needed for OHRM'S to get a reading. Because tattoos are technically a form of scarification, but one where the foreign body isn't expelled (ink particles), you're dealing with potential awkward readings. I don't mean wild interpretations necessarily, but complete drop-offs. Empty, with no data.

I have on my right arm in two key places (Upper forearm both sides and shoulder to elbow outside of bicep). Both are full black/gray shading) tattoos that I used to use my Scosche Rhythm +. Pre-tattoo, I never had a reading problem, maybe a drop-off from the signal here and there but not what I started to have after the tattoos. I'd occasionally have better luck with the forearm, but the unit just stopped getting a reading on my bicep altogether. It's a pretty full tattoo where there isn't much-naked skin there. It just won't get a reading there anymore.

And this is different than problems with skin pigment (naturally darker skin has more Melanin). There is no trauma, no foreign body that is affecting results here; this is just natural dark skin, It might just be a weakness of the technology there or a failure of the development of the technology in the first place. The ink itself might be the culprit because it is deposited in areas where blood flow the device needs to read, well, blocking it.

The type of ink used might be an issue. There is no universal type of ink artists use. Some use ink might have metals within them. I kid you not; I have a buddy that if I run a metal detector over his forearm, it gives a weak response. The amount of ink, how much transplanted to the dermis might just be obfuscating the blood flow outright.

It has been said above, but a chest strap used for activities is the more accurate option, but if your wrists are covered in tattoos, 24/7 monitoring (and sleep and stress) might be abnormal. I have only a right arm sleeve and wear my watch on my left. I also stopped using the Scosche due to the fit hurting my arms during workouts. Not trying to show off or anything, but even with the extended strap, it hurt my biceps. Too tight but too loose to get a good steady reading. I use the chest strap.

I hope this helps.