How do I model a digital out in a circuit simulation?
No, your sensor does not output 4V and 100 uA. It either provides an output of 4V and the current is determined by what is connected to the output, or it provides an output of 100uA and the voltage is determined by what is connected to the output.

In SPICE you would typically use a pulsed voltage source to simulate the detector output. After running the simulation you would verify that the output current never exceeds the maximum value (100uA in this case).

You really should provide a link to the datasheet of the sensor you are using.