We used Great Call for my dad. He wore a pendant that detected falls. He could also push the button on it. The operator would ask him if he wanted 911 alerted or just his adult children in the order we’d listed with them. It worked well for him and us
They make alarm "leashes" that attach to a person's clothing and then to the chair and goes off once they being to stand and the magnet detaches.
Or do you mean like a LifeAlert that contacts the control center, family and EMTs once someone has fallen?
More information is necessary to answer your question. Thanks!