With the safety beam, you know when someone "crosses the line". This high tech device creates an invisible infrared beam up to 60 feet long and sounds a loud alarm or pleasant chime when the beam is crossed. Not only can it be used as an invisible playpen to alert you when your child or pet leaves a safe area, it can also be used at night to scare off intruders. Retail stores and businesses can use the one chime feature to announce customers entering the store or the continous chime to alert them when someone enters an "off limits" area (in this mode the chime sounds continously until you turn it off). The continous chime mode is also good for alerting you when a child leaves a safe area. The distance indicator has a maximum distance of 60 feet and can be set to high or low. The volume of the chime can be set to low, medium, or high. Requires two 6-volt AC adapters (included) and three AA back up batteries (not included).  The dimensions are 4 and three-eighths inches x 3 inches x 1 and one-eighths inches.  Please note that this item works best when it is placed one foot off the ground or higher.