Here is something else to try. I was having trouble with mine as well. The classic alarm going off at 2 AM. I don't know how these things can tell when it is the middle of the night.
I read the literature and mine says to press the "test" button regularly. I did this and haven't had a problem since. I test it when I dewinterize just once a season. The tech guy said that dust can build up, along with spider webs and other outside nasty things and the test sequence can clear these things out.
If you have power to it you might want to at least give this a try before you replace it.