Sorry, I don't think any of the answers suggested are correct. The fob battery lasts a long time and the fob is generally on one's person or comes from the house; and to boot, replacing them does not solve the problem!
My 2004 Malibu key fob(s) had to be replaced several times. A hard push was required on most buttons. I looked inside before returning them for warranty replacement. There appears to be a broken solder connection which won't touch until a lot of pressure is applied--I've seen it twice. Because it was under warranty, I did not want to try to resolder, but I think that would work.
GM needs to toughen up the internals of this model of fob! While they are at it, they should know that the trunk open button sometimes accidentally gets pushed by other keys in one's pocket and should require being pushed twice in succession to operate. I also have seen my panic button activated accidently by other keys, and it should be further sunk into the fob case to avoid this. These design flaws may have been fixed in subsequent fob models.