Sending serial signal of HT12A encoder by wire over 25 meters distance
Use a twisted pair (one pair of a cat5e cable) or a shielded twisted pair if you are overly concerned, or convert to optical fiber if you are very overly concerned. 50/60 Hz is hardly ever a problem with unshielded twisted pair in practice. 

If you are running one of those "data over power lines" devices in the building you might have more reason to be concerned, as those put high frequency signals on the power lines.

I haven't bothered to look far enough into the data sheet to find likely data rates, but back in the days of modems (current for some folks, still) data signals ran for many miles on UTP cables at rates up to 56 Kb.