Ultra-sonic sensor conecting to Arduino

Hi! I bought one of those module kits to build an ultra-sonic sensor in order to use it as a motion sensor. It works well as its own, I mean, when powered by a 9V battery it’s integrated LED lights up when something moves in front of it, but what I would like is to connect it to the Arduino board so I can receive some kind of signal with it and make something out of it. The sensor has one line out to connect it with a Relay and I thought this line would also be able to connect to the board, but I already made some experiments and they all failed. I know it’s too much to ask, but do you think wou could look at the diagram I’m attaching and tell me if you think it’s possible?
Thanks in advance for the help!

Have you connected a meter to the Relay line out and ground and determined that something happens when the device detects motion? Whatever happens to this line when motion is detected should give some indication of the best way to connect it to the arduino.

Another possibility if the relay line is not working for some reason is to use the led your connection–either directly or through a phototransister circuit.

The relay line is the best bet though–until you measure the voltage don’t directly connect it to an Arduino input. If the circuit is powered by nine volts there is a good bet that the relay line is brought high and probably higher than the safe voltage for an arduino input. If this is the case a 5.1V zener diode could be used to connect the device to an arduino input.

If you have already connected the relay line to the arduino than check the arduino inputs with a simple test program and jumpers between 5V and ground to verify that no damage was done to the pins before proceeding.