Burglar Alarm a Bust

A week or so ago, I placed a burglar alarm in the alcove at the turn in our front stairs. I did it as an experiment. The front stairs is one of the main points where the weird in this house occurs. This is also the area where we most often pick up those photographic, transparent, disks that occur on photos shot during certain times of the year (Halloween, shortest day, Christmas, and on one occassion in mid-december). One day this week (Wednesday) I was working in the upstairs bedroom. We have a lot of extra furniture there that needed to go to the attic. I was in the process of transporting it the attic. The bedroom door to the hall stairs was closed but the door to the mainhall was open to the attic stairs. As I was working I heard a squeeking or grinding like noise, like something electrical that wasn't running quite right. I couldn't figure what it could be because we have very few things in the upstairs that run on an axis. I checked the bedroom and found nothing, I then opened the door from the bedroom to the hall to the top of the stairs and was blasted by that alarm. Ears ringing I made my way over to the alarm and hit the shut-off code. I then went downstairs through the open parlour door, through the parlour and opened the door into the diningroom where both my dogs greeted me. I went through the diningroom and into the kitchen where my wife was working on a project. I ask her if she heard the alarm; she said "No, and obviously neither had the dogs." She felt the alarm was no good because it was not heard all over the house. Thats a good point, but I'm not certain where I can find an Air Raid Siren to replace it with. And that still doesn't answer the question as to what set the alarm off in the first place. I suppose it could have malfunctioned or ..............?