My ds moved into his own room at 4 months and was still in a cot til the age of 2.5 when he climbed out! He's now 5.5 years old and he still calls out for us to come in before he gets out of bed. He can (obviously!) get out of bed himself, but rarely does it. But, we had a monitor in his room til he was 4 & it broke, but then we bought a video monitor for our new bub before she was due and we 'tested it out' in his room ... it ended up staying in there for months as our dd slept in with us.
I couldn't relax without the monitor. I sleep with a fan on and I simply cannot hear him calling out (his door has to be shut at night or he doesn't sleep). Even now, we sleep with his door shut and ours open at night and still at least 50% of the time my dh hears him call out before I do. But, I know now that at 5.5 if he really needs us he can come & get us.
I love the video monitor that we have for our dd who moved in her own room at 5.5 months. I sleep SO much better without kiddies in our room so she had to go to her own room by that stage. The video monitor means I can check on her easily at any time of day or night if she's asleep without having to get out of bed & go into her room, potentially waking her in the process.