Your key fob buttons may fade over time due to wear and tear from normal use.
You can reduce this wear and tear damage by using a key fob cover. Key fob covers (AKA cases, skins, jackets, gloves) slip over your existing key fob to prevent wear and tear damage due to drops etc.
If the buttons are worn the button pad in your remote would need to be replaced. This part can be purchased online done via your local locksmith or dealer.
Related blog post: How To Fix A Broken Car Key Fob