A "silent alarm" is a type of alarm that has no loud sound or noise when it goes off. It is designed to quietly alert someone, like the police or security team, without drawing attention to avoid alarming others nearby. Full definition
And you can set silent alarms to wake up to, although the vibration is pretty weak, and there's no way to adjust it on the band or in the app. (pcmag.com)
Sleep and activity monitoring are included, of course, along with less commonly seen smartwatch features like UV index info and a «nap mode» with silent alarm. (heavy.com)
There are several models, with features that include counting steps, tracking exercise, and counting calories, as well as silent alarms. (brighthand.com)