I have this little script that shows my problem. 

#!/bin/bash
sg_turs /dev/sr0 > /dev/null
RDY=$?
echo "RDY = ${RDY}"

This script always says the sg_turs commands exit status is 0. Even with the
door open and no disk installed.

The man page for the sg_turs command says:

EXIT STATUS
       The exit status of sg_turs is 0 when it is successful (e.g. in the case
of a mechanical disk, it is spun up and ready to accept commands). For this
utility  the  other  exit  status  of  interest is 2 corresponding to the "not
ready" sense key. For other exit status values see the sg3_utils(8) man page.