X10 SR751 Smart RF (Radio Frequency) Repeater Module Can greatly extend the range of the X10 Security Devices (Door/Window Sensors, Motion Sensors, etc) with proper placement Extends the range of X10 Hand Remotes like the HR12a and KR19A Has a Passthrough so you dont use up an outlet Any X10 unit that operates via RF Frequency can benefit from the Smart Repeater. This can be any Wireless Controller or X10 Wireless Security Component.