I came across this issue with Scottie. It happened when he discovered that the sound of his voice was kind of a ferocious loud sounding man bark (for such a small dog).
We also live in an apartment so I understand your concerns for the noise. It was frustrating at that time for me too - I was pulling hairs because every single noise from the hallway would make him bark. I even read into e-collars because I was *that* desperate. But upon reading more about it, it really didn't feel right. Personally, I didn't want to use that even as a last resort.
A few things I tried, which eventually made him stop (most likely, all in combination):
1) I played various Youtube sounds of doorbells, door knocking, elevator sounds, people talking, key opening door (you name it - they have all these sound effects on Youtube) and did some desensitizing training. Each time a sound was played, I'd give a treat right away before he barked. Then, I increase the time before he got a treat, if he remained silent. I did this on a very regular basis. It's helpful if you have a second person to play these sounds at the door, while you're somewhere else in your apartment to do the treat/clicker training.
2) I read a really useful post, explaining the usefulness of a dog who alerts you. She suggested allowing a dog to bark three times, then after that it's "enough"!
http://www.yorkietalk.com/forums/gen...h-barking.html
3) I also read about many members who found a water spray bottle to be effective. Some would argue this is not positive reinforcement training and that it shouldn't be used. But, this was my last resort. My bottle sprayed a mist, not a stream of water. I believe it was the bottle or the spraying sound that deterred him. I actually only had to use the bottle twice, in combination with the command "that's enough", followed by a lot of treats when he stopped barking immediately, and he finally figured it out.
I read about another technique that I didn't manage to be able to do: train your dog to bark on cue. And then train your dog to stop on cue. I think if I was able to do that, it'd be pretty useful. But it was a little more than I could handle.
Also, we tried the penny in a can. That didn't do much for us. But every dog is different.
Good luck!!