DRH-301-V4.2 App use to work with DRH-301-PWR, DRH-301-V4.2 and DRH-301-V3.2 GSM power socket. The app auto edits and submits SMS content and commands to the socket. With the APP, easy to operation and configuration of your DRH-301-PWR, DRH-301-V4.2 and DRH-301-V3.2 power socket.