board has 8 analog(balanced) and 1 digital(unbalanced) ports. Analog ports are hybrid, meaning that they can be switched in software to unbalanced. Connection can be established via wire(RS485) or radio(RFM69). It has onboard relay and similar power detection circuit as gateway. There are 2 free pins left that are taken out to allow some user application like additional relay board.
The relay present on expansion board can added as basic relay output, or it can be registered as remote Horn/Siren, by the configuration definition described in expansion board sketch. Also new functionality was added into gateway firmware, which is now able to recognize such remote Horn/Siren nodes and turn them on, when associated group is in alarm state.