Arpwatch for Yosemite? Any pointers to arpwatch or equivalent for OS X Yosemite?  I'd rather not have to  use Macports. Sledge hammers on gnats etc.  I found one, Mocha, but it requires a version of Java 6. Current Java version is 8, and I recall 6 having all sorts of security issues.

This arises as my MacBook Pro is detecting another device using it's IP address.

Command line version is fine.
You can simply right-click /Applications/Mocha.app/Contents/Resources/Java/mocha.jar and launch it with the Java Launcher. I don't know if the JRE version contains this "app" - at least the JDK does.

After modifying the innards (e.g the info.plist &amp; JavaApplicationStub) it may also be possible to launch the app itself without installing Java6, but I didn't get this to work.