The H0300 connects to the M1000, M3000, M4780 and the H1500 by the means of a common two-wire RS485 bus cable. The maximum length of the bus cable is 1.000 meters; however RS485 compatible repeaters can be used for extension. The H0300 can survey a total of 63 units and it provides instant visible and audible alarm should the communication fail to any one of the connected units.