Does hd-idle check if the disk is idle prior to spin down the drive?

I was thinking about to let hd-idle manage the spin down of all my drives after 3 hours because I am having trouble doing so with hdparm or smartctl in conjunction with apm or sleep command. ___ So my question is: Does HD-Idle check if the disk is in use or idle prior to send it to sleep? And in case it does not: Do you have a nice solution or script that I can copy / modify to my needs?