It looks like the interrupt control variable was changed to DS3231_CONTROL_INTCN from DS3231_INTCN in the library header file in the following commit/merge: https://github.com/rodan/ds3231/commit/6448c033b721b0e0a3017375099623d7e00785d3 Changing the DS3231_init call to use DS3231_CONTROL_INTCN fixed...