Lumo Lift is a "Posture and Activity Coach" made by Lumo BodyTech that you can magnetically attach to your shirt, right next to your collarbone. It has an accompanying app for iOS and Android and a Windows desktop version and retails for $79.
The Lumo Lift is well-designed: small, modern and light-weight. I could wear the white-colored sensor with any outfit, and people would either overlook it or think I'm wearing some sort of pin, which is nice in a world of intrusive & clearly visible wearables.
While wearing Lumo Lift, I appreciated how much I was aware of my posture. Even if the Lumo Lift didn't think I had good posture (more on that later), I barely slumped while it was on my body, and had better posture for longer periods of time than ever before. Every time the Lumo Lift detected poor posture, it would buzz, so my goal for better posture also meant fewer buzzes and less distractions.
Unfortunately the Lumo Lift lacks context. You don't get information how you need to improve your posture. The sensor fails to live up to its "Coach" persona: If I can't pinpoint where my posture needs room for improvement, it's probably not going to improve.
On top of that you can't turn the device off, it just keeps on vibrating, and the step tracking is inaccurate.