The find command could be used as well. As in:
find {PATH} -name {FILE} -size +0 -exec {NOTIFY} \;
which I believe will only search the PATH for the FILE and will only run the NOTIFY command when the size is greater than zero. You could put that in a cron script described by PSD above. The benefits that find has over ls | awk are only a single command instead of two, and it would use less resources (I may be wrong - but calling awk for a simple one line check is wasteful).
Anyhow, I hope you find your answer.
Einstein47
(Love is like PI - natural, irrational, endless, and very important.)