Re: Graco 2791 Monitor. It appears that we have successfully locked in the parent unit to the Nursery Unit but upon testing, there is no sound. We have tried numerous attempts to lock in again without succees. When locking in, the red light turns green and when the Nursery Unit is turned off the parent unit Led turns red and begins to beep. Also, when both units are close together there is no shrilling indicating that the units are too close together. Please advise. Claudia