UPS is 5v. So use logic level converter.
Edit: they are back from holidays."The alarm contacts on the Eaton MPS12-30 unit are open collectors with a component such as a transistor or similar as part of the integrated circuit."
Testing on the alarm pins on the UPS, when the UPS was on battery, showed no voltage on any of the pins using the alarm signal return pin as -. Tested again using alarm signal return pin as +. Still nothing.