If you follow the advice given in the article you should be able to locate it -- probably a bug sweeper will be sufficient. I guess you must be on talking terms with him to suspect he is spying on you? One way to tell if he has bugged you is to have a conversation inside your home about something that you would not normally talk about. Let's say you start talking about going on a cruise or something. Keep talking about it. Make plans. Pretend it's really happening. Then if he repeats the information back to you, you know for sure he's listening. If he doesn't mention it, try something else. Talk about a new car or having work done on the house. See what happens. If he never repeats any of this stuff back to you (or via another neighbor), then your fears are unfounded. You can rest easy.