Life-bit, Heartbeat, Watchdog, BEX-Modul

My PLC device or better the main PLC I don’t have, has a BEX-Modul.
I searched the web with no results.
In my manual, I recently found the meaning it’s a “Befehlsausführungsmodul für extern angefordete Befehle”. I also haven’t found that on the web. Also not on other PLCs from Festo.

When the programming device is attached (to the bus), there’s a steady signal sent. If there’s no answer within 4 seconds, there’s a busy flag (Merker) set, an error displayed and predefined measures take place.

The first I found on the web is a life-bit (in German Lebensbit). Probably mainly or only used by PLCs.
I then read about Heartbeat.

It obviously depends on the bus standard. Monitoring of the interfaces. PLCs also check for other details (temperatures, voltages, errors on every card etc).

Has anbody heard of life-bit before or has experience with similar stuff (on other PCs or devices)?
For what peripherics does this make sense. A printer? Or is it just timeout after some time?

I also don’t know how this is done on my machine. How do the PLC know if a device is attached. Hot plug?