That means - you press a (possibly virtual) button and an LED lights up someplace else.
https://www.youtube.com/watch?v=OhnxU8xALtg
Arduino, HC-05 bluetooth module, breadboard, processing, sketch, blue control Android app
Google search that was useless : "what is the easiest way to get a notification on your phone from a device at home?"
Another one "do you need a subscription to get notifications from home kit devices?"
