Originally Posted by
Silk
Part of what my group does is to test TCAS after its installed by another group. On our aircraft, you'll hear "Traffic, Traffic" when you're 6nm away from other aircraft at your altitude. If you hear "Descend, Descend" or "Climb, Climb", you are within in 1nm and should probably be a little more concerned.
It's not distance, it's time. The actual distance when a TA or RA is triggered will vary based on the closure rate.