Is it better to use input_pullup or have arduino measure the voltage?

Projects General Guidance
1

So I'm trying to hook up a harbor freight driveway alarm to an Arduino. I found a place on the board to get the input from. It measures 0V when not triggered and 0.72 V when triggered. Then just for fun I decided to measure the resistance and it seems to be 1000 ohms when not triggered and 0 ohms when triggered.

So my question is is it better to have the Arduino measure the voltage and use that as the input, or is it better to use pull up resistor as the input?

Thanks!

Also follow up question, how do you know what is the best place on the board to get the input from? I picked my spot based on the fact it's close to the LED's on the alarm, and they light up whenever the alarm is triggered. So i figured that that would be a good place to start from, but I really have no idea. (Please see attached pic. I soldered a green wire to that spot)

IMG_20181028_0042434.jpg
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2

Use the pullup, unless that interferes with the operation of the circuit. Given that you're basically tapping into the LED indicator, I don't think that will be a problem.