At My Wits End with Mysterious Beeping Noise--Please Help!

I am at a loss trying to figure out what the beeping noise in my apartment is. I initially thought it was coming from my hard-wired smoke detector, but I've disconnected the detector and the problem STILL persists! (My apartment is located in someone's house.) The noise I'm hearing is NOT a short chirp, rather a single, very LOUD beep that makes me jump out of my skin and sometimes wakes me up in the middle of the night (depending on what time it goes off, which I can never predict). It happens frequently and there is no rhyme or reason as to its pattern. Sometimes it will happen once a day. Sometimes once in the early evening and then in the early morning. Sometimes at 10:00 or 11:00 PM. Sometimes at 2:00 or 3:00 AM. Sometimes it will skip a day or two. Sometimes it will happen for several days in a row around the same time. Other times, it will happen at a completely different time of day/night. The beeping problem usually lasts for a few weeks, stops for a week or so, then starts up again. The only other thing I can think of is that there is a carbon monoxide detector behind the door that connects my apartment to my landlord's house. The boiler is also behind the door. Said connecting door is locked, so I do not have access to the carbon monoxide detector or to the boiler. Could it be the carbon monoxide detector going off because it's near the boiler? My landlord does not hear the beep going off. The area in which my apartment is connected to his house is next to a remote food pantry that he and his wife seldom go in, far away from the areas in his house where he and his wife usually hang out. The carbon monoxide detector and boiler are located in this remote pantry. Why? Beats the heck out of me!