How to invert 'watch -b'?

I'm trying to get my terminal to alert me with a simple bell once my domain registration has finished (is resolvable). From watch --help: >Options: >-b, --beep beep if command has a non-zero exit How can I invert this option, so it beeps if the command has a zero exit? I also tried variations of the following, but I can't get it to beep when inside watch. watch 'nslookup foo.bar && echo "\a"'