I finally replaced my old phone last week and opted to go with the S9+ because it has the built in Heart Rate Monitor (HRM). This was useful for being able to measure Heart Rate Variability (HRV) without needing an external, specialized HRM to do so.

I was also intrigued by the HRMs purported ability to measure blood pressure, which is a new feature. In the past you needed a blood pressure cuff to measure blood pressure.

Here is what I have learned so far:

1. There is only one app (as of this writing) that can use the blood pressure technology for the built in HRM. That app is the My BP Lab app. You can find it here. This is a wellness focused app (akin to Welltory), so it does other things in addition to measuring blood pressure. The app used blood pressure along with other health/stress informaiton you provide to make lifestyle and wellness recommendations. I don't have any recommendations yet, so I don't know how well it works. You can use the app without the S9 HRM, but you need some other way to measure your blood pressure.
2. The sensor currently requires you to input an initial blood pressure reading from an external source at the same time that you take your baseline reading using the HRM in the device. Without the additional baseline reading it can only measure differences in blood pressure as a % change from the baseline.

The ramificaiton of number 2 is that it isn't really capable of measuring blood pressure, it's measuring something and then it can measure differences from that. Those readings and changes can be interpreted into a blood pressure reading as long as you have an initial reading to go along with the baseline. It's still neat in my opinion, just something to be aware of.

It may that this changes over time and as they collect more data (from Quatified Self nerds, such as myself) they'll be able to do blood pressure directly. I'm interested to find out.

I've been using the app for about a week and I had to do one recallibration using my Qardio blood pressure cuff.

The early morning reading I got from the app seemed off to me. I double checked with another device and it was off. So I re-baselined in the app. The app allows you to do this, which seems like a good feature and also possibly a bit telling.

I don't know how it handles previous measurements if you do a rebaseline. It certainly seems to call their validity into question. I'm pretty sure that, at least for the app's purposes, it is going to assume their correct and keep them around. I don't have any reason to feel that other, earlier, readings were off. They seemed in line with what I got with Qardio throughout the day, though I wasn't comparing them side by side every time.

Yes, I own a Bluetooth blood pressure cuff. Why wouldn't I?