Fibaro UBS potential-free - Potential-free contact with 12v power supply.

Hello
I would like fibaro to inform me when there is no power supply in the house and here is a small problem. I have connected the Uniwerasl Sensor Binary to the UPS. I tried the GND connection from the other power supply, but it doesn't respond (it only responds to the GND of the UPS, there is a change of state as the contacts are shorted or not, but that doesn't help me at all)
I don't know how to solve the problem with the potential-free input. I would like, for example, to be able to change state with a second 12v power supply. That is, power is NC, no power is NO or vice versa. I also need this for the bell, which is on 12v
I have reed switches connected like this (like the rain sensor in the picture) and it works very well.



Added after 31 [minutes]:

Will a relay module e.g. PULSAR AWZ510 12V change my state e.g. from NC to NO in case of power failure/appearance on this relay?

You need an optocoupler. You power the optocoupler diode from the 12V power supply using a resistor - you will calculate what value you want the resistor to have based on the optocoupler datasheet. You connect IN1 and GND from the Fibaro UBS to the other optocoupler pins. When voltage appears on the 12V power supply, the optocoupler diode will light up, switch the phototransistor and connect IN1 to GND in the UBS and you will have a state change at the UBS input. In this way you will have such an electronic relay, which will further galvanically isolate your 12V supply from the UBS circuit.