Over its 15 year history MindBlog has done several reviews of widgets currently on the market that are meant to monitor and relieve stress. Chiu has done a review of three current devices you might have a look at if you have $250-$350 to burn. It seems that most users find mild benefits when trying them, but don't feel a strong urge to continue using them. The online reviews offered by vendors are predictability ecstatic (placebo effects anyone?). There is no peer-reviewed research from large-scale clinical trials of their efficacy yet available.
The Appolo Neuro is a slightly curved rectangular box on a band that can fit around wrist or ankle and issue "soothing vibrations that speak to your nervous system" to increase heart-rate variability during normal activity and sleep... Hmmmmm. The other widgets are used in sessions that are set aside from daily activities. The Sensate 2 looks like a smooth river rock that is placed on your chest during sessions and "combines vibrations, or “sonic frequencies,” synchronized with specially composed soundtracks to enhance relaxation." The Muse 2 is a meditation headband, which has built-in sensors monitor brain waves using “advanced signal processing” to translate brain waves into sounds of weather.
I tried similar widgets 5-10 years ago. This time, I don't think I'm gonna go there....from Chin's article: "most people don’t need wearables or technology to effectively manage stress,... Before investing in a device...why not try well-established, free approaches, such as spending time in nature, exercising, practicing mindfulness and cultivating social interactions.