Monitor input while Move

I am currently writing my first RAPID program so I have limited knowledge on the RAPID instructions.

I was wondering if there was a way to monitor an input while executing a move instruction.  In my application I am picking up a tray with my robot and placing it on a stack.  I would like to be able to determine if the tray has fallen out of the gripper whilst moving so i can stop the robot and set a fault bit.

Help is much appreciated.

Cheers