Initial thoughts on a £18 Colmi R09 smart ring and Gadgetbridge

I bought a Colmi R09 “smart” ring from AliExpress, and I’ve been giving it a try for the last couple of weeks.

For £18 (being AliExpress, the price fluctuates a bit), I didn’t have particularly high expectations, and I have been pleasantly surprised.

The ring

The ring is slightly concave, and black.

It does not stand out / look unusual, although when it takes some measurements, the LEDs pulse on the underside of your finger, which I guess could be visible.

This one has no screen or other human interface.

I have worn it every day since I received it, and no-one has commented on it / asked about it.

In terms of build quality, I’m impressed. It feels reasonably robust. That said, I’ve been taking it off when I have been doing my boxing exercise, even though I wear gloves.

The Colmi website says that it has

5ATM water resistance, making it suitable for swimming and other water-based activities.

I have not tried swimming in it yet, and I’ve taken it off when I shower (but not when washing my hands), but it seems that it should be fine for both.

I don’t wear rings generally, so I’ve had to get used to having something on my finger. This ring is light and comfortable. For someone used to wearing a ring, I imagine that it would be fine.

I measured my finger in the way suggested (a strip of paper, then measure the paper), and it is just about right. I wonder if the slightly smaller size might have been better, as I can easily rotate this ring, which means that the sensors are moved out of place), but then I wouldn’t want something too tight. If you know your ring size, again, this might easier.

The ring’s battery lasts for about 6 days, with it set to monitor my heart rate every 10 minutes, which I think is impressive.

It comes with a small black charging box, which has its own internal battery and a USB-C socket. To charge the ring, one places it on the mount in the box. I found I had to put the ring in place in one particular orientation so that the red charging LED comes on; the other way round is flaky. Charging the ring takes about 45 minutes (roughly; I forgot to measure it).

I’ve never seen a connector like the one used on the ring, and my feeling is that, if I lose or damage the charging box, I’ll end up buying another ring and box.

Someone has had a good look at the firmware of a very similar ring.

It works well with Gadgetbridge

There is apparently an official app to use with the ring.

I have not used that; instead, I’ve used the excellent open source Gadgetbridge software on my phone running GrapheneOS / Android. This stores the data locally, and I don’t need to (or want to) share it with any third party.

It connects using Bluetooth, and paired and connected easily.

The Colmi R09 is well-supported by Gadgetbridge.

It can monitor and report on:

• steps (but - like every device I’ve used - this does not work well on a cross-trainer)
• distance (based on steps, I think; it does not work when I am cycling)
• sleep time and quality (and this is the first device I’ve found comfortable enough to wear while I sleep)
• HRV status (not sure what this is)
• heart rate (and you can set within Gadgetbridge how often you want it to monitor for this)
• stress (I don’t know how this is calculated)
• speed zones (no idea)
• live activity
• blood oxygen
• temperature

As far as I can tell, the only unsupported function is firmware updates.

I sync the ring to Gadgetbridge manually. Apparently, the ring has enough storage for about three days’ worth of records.

I have not benchmarked accuracy

This does not bother me, but it might be a deal breaker for others: I don’t know how accurate it is.

For me, it is more about trends than the accuracy of any individual reading. Am I consistently doing a similar level of exercise, rather than exactly how many steps I am doing.

I wear a PineTime watch on the same arm, and the stats shown from the watch are sometimes consistent with the ring, and sometimes miles out.

I should probably try to benchmark the ring against a dedicated pulse oximeter, but ours has gone missing…

Final thoughts

Overall, for the money, I’m pleased with it.

I like the fact that I don’t need a specific app, or to share my data with a third party.

It feels a bit futuristic and, while I’m still getting used to having something constantly on my finger, it is reasonably unobtrusive, and measures a useful range of things.

I kind of wish that, like my watch, it vibrated for notifications. That would be useful, and I’d happily trade off battery life for this. Other rings in the range have a screen on them but I don’t think that they do notifications either.