The unit I wore had a wireless interface and when it detected something unusual, such as me walking up a hill, it would alarm and event and try to make a cell phone call to the base station. It asked that I characterize what was going on: e.g., exercising - so a faster HR is expected/normal. If I was not in a cell phone range it asked me to make a telephone data set call to pass the data to the base station as soon as I could.
I've heard of others that had this type of monitor. I guess it senses an arrhythmia even if you don't and will record it. I've never had that type. Mine were always a do-it-yourself type.