The happiness of the cat depends on their individual preferences, but all the research shows that indoor-only cats live much longer with many fewer health complications. Mine would love to explore outside, but is content enough to watch the birds from the windows. She has had a collar for so long that she barely notices it, but I keep it on because she has occasionally made a dash out the door. I think avoiding fleas, ticks, and cars is plenty of reason to keep her inside.