Weechat used to require some weird perl scripts to trigger on specific conditions, but since version 1.1 (from 2014) a trigger plugin can do all that without needing an external script.

This will create a trigger that runs a command when a specific word (or words) is mentioned in any channel you’re on:

/trigger addreplace warningword signal *,irc_in2_PRIVMSG "${message_without_tags} =~ (danger will robinson|stop the line|help me)" "" "/exec -bg /usr/bin/paplay /usr/share/sounds/ubuntu/notifications/Positive.ogg