The GSM Relay Rev D is a GSM based control module, controlled via SMS with 2 inputs and 1 Relay output. The main usage for the unit is to reset router boards which have became inaccessible through wireless networks as well as informing the user about mains power failures and other alarms such as low battery conditions. The GSM RELAY D features high and low configurable temperature alarm settings as well as the included temperature probe. However it can be used for various different applications at home or at the office, such as controlling other electrical equipment, monitor the voltage of your battery backup systems and so forth.