What are the key differences between open and closed lone worker safety programs?

I'm uncertain because I haven't heard the terms open/closed in relation to the safety programs, but I expect that it has to do primarily whether the safety device prevents risks locally (closed) like a two hands required to run the machine switch, or summons help when danger is detected (open) like a dead man switch that needs to be acknowledged every certain interval or it's assumed the worker is unconscious and help is summoned, if it's like other systems that are open or closed.