Keypad chirps stopped working

I have 3 keypads and I have 2 of them set to "chirp" when a door or window sensor is opened. It's been working great for months but yesterday all 3 just stopped, even though I've made no changes to the system. The base station still chirps, but not the keypads. And the keypad buttons no longer make any noise - has there been a firmware update gone haywire?Both keypads set to chirp, volume on high, all sensors set to chirp on the open event.