This is an important safety feature. A firing fuse is required on each SmartRail before any cues can fire. These fuses are not intended as any current protection like most fuses. Instead, these fuses serve as a cheap but effective switch. These fuses are analogous to the keyed arming switches found on the firing modules of many professional systems. These fuses are kept in the possession of the lead operator until showtime.
Heartbeat refers to the signal that is routed through the deadman switch and then broadcast on the RS485 bus to all SmartRails. This heartbeat is considerably faster than a human heartbeat -- 1000 times per second. If the deadman switch is released then the heartbeat stops and no more cues can fire on any SmartRail.
The memory on-board a SmartRail will remain valid even if power is removed. This allows SmartRails to be programmed for a given show weeks in advance.
RS485 is a communication standard that allows devices to be located great distances apart from each other. RS485 requires a twisted-pair of wires to achieve reliable transmission up to 4000 feet, or even farther with repeaters.