Key pad 9827 with control panel 9800 suddenly went off showing bF?

My key pad 9827 with control panel 9800 suddenly went off while I was indoors and it had not been set. It showed In red bF. It has done this twice 10 minutes apart.
I have checked all the alarmed places and the motion light is still coming on.
Why is the alarm going off when it has not been activated?
Would you please tell me how to rectify this?
I am not alarm savvy and would appreciate your help.
Jo