Call the fire department, they have detectors that they can use to look for gas leaks and other things that can set off a detector.
You can also call your gas provider. One of those two should be able to track it down, it could be a lot of things, but two different smoke detectors going off in the same location is a huge red flag.
Best case, you have something kicking up fine dust, worst case, you have a smouldering electric fire in your wall somewhere.