Because I specialize in post-production work I often work much later than my co-workers and it’s not unusual at all for me to be the only person in our entire office late at night or even overnight.One night, well past midnight, I was dealing with a difficult technical issue and getting frustrated as I was tired and wanted to go home. After slamming my hands on my computer keyboard in frustration, I went to get a glass of water and take a break before I broke anything.As I left my office, I heard someone whispering *directly* behind my back.Our office at the time was a big open concept loft - I had the only fully closed off office and the other “offices” only had partial glass walls - the rest of the floor was just a big bullpen of IKEA desks with just legs and tabletops. It took, at most, 20 seconds to survey the entire floor end-to-end and confirm that there was no *possible* space anyone could be hiding. I just chalked it up to a mistake, got my water, and went back to work.Shortly after I sat back down at my desk I heard the whispering again. It was coming from *right* outside my door. The words were so indistinct I couldn’t quite make them out, but this time I got a clear impression it was English and a young, female, voice. The instant I turned trying to see who was there the voice immediately stopped. It was completely unnerving. Spooked, I turned on every light I could find. I looked over everyone’s desk to see if any computers were still on or any phones were off the hook. I even went down to the only other floor of the building to see if the downstairs tenant (who was almost never in the building) had decided to show up at 2am. Of course there was no one there - and I could see from the security panel at the door that their heavy-duty alarm system was on, including the motion detectors. The front doors were locked tight, the fire escape, stairwell and bathrooms secured and empty. I was, demonstrably, the only person in the entire building.Convinced, I went back to my office and opened my notes to refresh myself on the technical problem I was supposed to be solving. After a few moments of writing I suddenly heard the voice again - but this time saying clear as day: “he’s using Microsoft Office” - the program I had just switched to!I turned the office upside down trying to find out what was going on. I searched filing cabinets and desks for hidden speakers, looked for concealed cameras, checked the street in front of the building (and the roof of the building opposite). All to no avail. I was starting to think I was losing my mind.Finally after I combed every inch of the main office for a third time I conceded that, given my fully enclosed (no-window) office, and every check I had just done - there *was no possible way* anyone could be seeing what I was doing on my computer screen. This was clearly just a figment of my tired brain running wild.I walked back to my desk and sat down and the voice immediately whispered: “now he’s using Firefox browser” (which, again, was true).Thankfully - instead of running in gibbering madness into the night - a light-bulb suddenly went off in my brain as to what was going on - and it turned out I was correct:When I had slammed my hands on my computer in frustration earlier - three things had happened that I didn’t realize or intend:My earbuds, which were still plugged into the headphone jack of my computer, slipped behind my desk.I turned the volume up to it’s maximum level.I accidentally hit the key combination to turn on the “voice assist” built into my computer to dictate to those with vision loss.So.. whenever I was actively typing, or clicking on things, the computer was helpfully dictating everything I was doing in it’s female computerized voice. Because the earbuds are such small speakers (and were dangling behind my desk, slowly rotating around) most of it was inaudible except for the odd word or phrase that, after reflecting off the bottom of my desk and the floor, sounded exactly like it was coming from just outside my office door. Aside from the actual names of the programs - my brain was just filling in the rest of the indistinct narration. And of course, the moment I *stopped* using the computer (as I would do the instant I thought I heard something) the dictation would stop‡ until the next time I sat down and started typing again.I don’t think I actually ever did solve the problem I was supposed to be dealing with that night - but I figure solving one huge, impossible, mystery a night is probably good enough.