...you shouldn't have to respond in home hours regardless. Any time you spend on work during your life outside of contract is them stealing your labour.
Many IT jobs require an on-call rotation. Even when not on call, an SME can be called in an emergency. Time spent on call-outs typically either pays overtime or gives comp time. The infrastructure has to keep running, that's just how it is.
I keep critical applications running at work that thousands depend on. While I was at a union convention, one of my apps broke. I had to login that day and fix it while going over the budget with other members.
This is how the IT world is. I'm the only person capable of maintaining it and I must be available if things go wrong. The show must go on.
many people who work from home have flexible work hours (they can decide if to work in the evening or morning) and so they need to be reachable at any time, even it it might be off hour
Kinda. I set my office hours in outlook, so people see if I'm available.
I mostly don't actually work at unusual times. But I can, if necessary. What's more important is that I don't answer work calls outside my hours, unless it's one specific co-worker or I know in advance that a certain thing may require my attention.