Meaning it failed to detect a drop in oxygenation? Unless it fails 100% of the time, it would still be useful since “alerts on some non-zero percentage of life threatening conditions” is better than the alternative which is no alerts at all.

We had one and I think it made one or two false positives where basically it fell off. I can’t say anything about false negatives since none of our children stopped breathing. (It had two alerts, one for losing skin contact and one for low oxygen. The first one we got all the time when forgetting to pause the base station before removing the sock, so that bit certainly worked.)