If it shows up in Cayenne as an online device (like in my blank dashboard image, without a yellow banner saying the device is offline), you could check that way. Otherwise you could try the solution in kreggly’s post to enable software serial to see debug output which could help you determine this.
If you have access to the router admin, the simplest way might be to look for a list of connected devices. Most routers I’ve owned have had a page like that in their web interface where you can see a list of each device currently connected.