Here at CES, I am in desperate need of relaxation, so I gave it a shot. Sadly, a quick demo isn't really enough to say if it works, but the Doppel team says it has research on its side, including a study published in the peer-reviewed journal Nature Scientific Reports. I am no scientist and cannot vouch for the study, but it's at least good to see that Doppel is aware of the need for some scientific evidence to back up its claims.
Naturally the Doppel syncs with your phone over Bluetooth; from there you can set up different rhythms for different moods and choose between them. The device also has a touch-sensitive front for swapping between two different rhythms without needing to use your phone. The touch capabilities were definitely hit-or-miss, and Doppel's head of marketing Georgina Orso admitted it wasn't perfect -- but she also said they were pushing software updates out to improve the device over time, touch sensitivity included.
Beyond some peer reviews, the Doppel has actually been in the wild for years now. The company first launched it with a Kickstarter in 2015, but Orso notes that it was the sort of Kickstarter where the company wasn't selling a finished product -- it took all the funds to go into manufacturing for the last few years and took user feedback into account to continue improving the device.
After all the years of development, though, the Doppel is finally ready for a wide launch -- it'll be available on the company's website today for $219. That's not an insignificant investment for a single-use device, but if you're the kind of person who needs help calming down it might be worth a shot. The company also offers a 60-day return policy so you can try it out for a while and see how it works before committing to it.