When the Apex comes out of the box, and is first connected to your network, it will attempt to get a dynamically-assigned IP address from your router, just like your computer, smartphone, and other networked devices. With a display, it's easy to see what that address is by scrolling through the menu. Without a display, there are several methods, but I'll only describe the two easiest.
The Apex will respond to a name of 'apex' (with Windows PCs only, not Macs), so in your browser, you can just type
http://apex. Once the Apex web page loads and you log in, you can see the current IP address on the Network setup page.
You can also use the Apex Flash Utility. With the Apex Jr, it comes on a CD. I don't know if Neptune has started or will start shipping Apex and Apex Lite models with the CD, but it really doesn't matter... you can download it from Neptune's web site. After you download & unzip the file, then run the Apex Flash Utility, there will be a magnifying glass icon. That icon, when clicked, will launch a discovery process and display the results a new small window listing all controllers found. The IP address is listed there.