Prometheus metrics (using pg_up)

I am using below query to find filesystem usage. It works good but i’d like to implement the alert on select filesystems.

( 1 - (node_filesystem_free_bytes{device!~'rootfs’} / node_filesystem_size_bytes{device!~'rootfs’})) * 100 * on ( node_name ) group_left pg_up

Any idea how to do that