The ID3 button is also called the Public ID button. When held down during power up, it selects the Public ID, code 999, on an RC4Magic device. This button serves other purposes after the device is powered on and is running normally. ID selection only happens when a button is held while power is applied to turn it on.
RC4Magic devices are programmed with 4 system ID codes. Three are private and unique for every owner, operator, or project, and the fourth is the Public ID. The Public ID is the same code on every RC4Magic device every made, allowing devices from any system to communicate with devices from any other system. The other IDs, Private ID0, ID1, and ID2, only allow communication between other devices with those same private codes. No other wireless DMX system from any manufacturer provides this level of data security. Even operating in the same room, multiple RC4 users can never functionally interfere with each other.