Boop
The first result on google generally does the trick.
What you do in your own time is none of my business, but eavesdropping is totally unethical in my book. Not only that, but
if you get proof of anything illegal going on you can't actually prove it without getting slammed for monitoring their conversations...and they still probably wouldn't do anything after that.
Not that it really matters, I doubt that a conventional scanner would be able to pick out any conversation next door from the other hundreds of frequencies -- not to mention the fact that cellular phones actually use two different frequencies, so you'd only be able to hear half of the conversation at a time.