I'm not an expert on it, but my three attempts were with a belt hanging from a doorknob. It didn't work for me because I aborted mid-attempt.
The gist is that it can work, but it's less effective than a regular rope. I've read that it has to do with a belt being flat - the pressure isn't even across your neck. In my experience, the edges of the belt really dug into my skin and I found it super unpleasant.