Wireless Interference

The system works as it should. They only problem I am having is the keyfob will not work at all or it will give me a wireless interference when I hold the button down for a few seconds trying to get it to work. This is the third keyfob I have gone through. They work fine for a couple of months after I get them and then they go dead or start giving me that message on the keypad. No, I have not gotten any new appliances or devices that could interfere with the base station or fob. I have moved the base station elsewhere and still the same problem. The firmware is up to date.