Check the detector's User's Manual for the warranty period. If it is out of warranty (the one in our RV was one year), call the manufacturer. They may make it good since it is only out by two months. The manual for ours states that you can press the reset button and clear the warning, but it will come back after 72 hours. After 30 days it won't reset. The lets you use it until you can get another one, but I don't know how reliable it would be during this time.
By all means, replace it as soon as possible.
The original one in our RV failed before it was two years old. The life is stated to be five years.