How to read high impedance on pin arduino?

Hi!

The goal is to catch an AC leak. For these purposes, I use a measuring transformer (RCMB121). When there is no leakage, the output contacts are low (GND). If an accident occurs, the contacts go into a high impedance state. How can I read high impedance condition with Arduino UNO? As I understand it, this is not a HIGH level. Can I pull these contacts resistors (10k) to the power line?

Google "open collector".

Use pinMode (pin, INPUT_PULLUP)