What is the HAT bus
From Safe Intercom - Technical Support
The H-series devices have a modular design that allows you to connect expansion modules with each other. The HAT bus is a specialized 1-wire protocol designed to enable two-way communication between all Safe H series devices connected to each other. Communication takes place with one wire, which is on the yellow cable on the 3-pin connector. Each slave device needs also power cables (GND and 12VDC). Everything is handled by easy installation on JST plugs.
HP6 and HP3 modules should be connected with master devices with 3-PIN JST 1.5mm cables:
HWK and HWKL modules need more power and should be connected with 3-PIN JST 2.5mm wires:
