How effective are the no bark collars.

Thirdly, the citronella does go away in a short time, and if the dog isn't chained to a tree or something, he can move out of the general area and won't have to continue to smell it - unless he barks, of course.

I crate one dog, and confine the other to a small room, while I'm not home. Perhaps that's why I'm so opposed. They CAN'T get out of the cloud of scent. Of course, we don't have a barking issue. At least, we don't have anyone complaining[]

If you don't actually know if it's him barking, you might want to try to find out first. If there is someone who you trust living near you who is home during the day, that would be cheaper than having to set up a camera. Another option might be listening for yourself from outside your condo. It might be possible on the weekend. Have him believe you are out, stay somewhere where he can't see you, find out if he barks at all, all the time, or just when certain things go by.
Just to add, we tried those boxes that plug into the wall (I think they're called Bark Free)  and  they didn't work at all. In fact, it made Max bark more. He'd bark at one thing, and it would go off. I guess it must of bothered him, because he would then turn and bark at the bark machine. He didn't seem to get that when he stopped barking, the machine stopped making noise. I tried it on the settings that only the dog is supposed to hear, and the tone that people can also hear, and both agitated him into barking more. It seemed to make no difference at all for Millie. She just kept on barking like the thing didn't exist.