We have a smoke alarm that started giving us random false alarms in the middle of the night last week. So finally we just took it down and ordered a new one. Well, brand new smoke alarm went up on the wall yesterday, and what do ya know, 3AM, more false alarms ... I'm stumped - it's not a particularly dusty area, it's right in the main stairwell of the house, about 2 meters off the ground, and there was nothing at all that smelled weird in the slightest.