Constant-on, you will get that alert long before it's your turn in the crosshairs even with a marginal detector. Instant-on is the issue - that's where good, long-distance alerts that a quality machine, like a Redline or well-tuned V1, will help. I've had an instant-on hit from over 8 miles (rural New Mexico, flat land and the guy was in a depression in the median, almost totally invisible until less than 100 yards away) on both of these units... just enough to let me know there's someone way ahead sampling traffic.
Now, if you're the only possible target for a very long distance, or in heavy vegetation, rolling hills and around corners from the shooter, you will probably be toast. There are dozens of winning scenarios for verbal interaction, but I've had decent luck with honesty - "such a nice day WITH GREAT VISIBILITY, beautiful road WITH NO TRAFFIC, I didn't realize I was going too fast FOR CONDITIONS. I usually have traffic to sort of gauge my speed to, but WITH NO OTHER VEHICLES OUT HERE I guess I let it sneak up on me a little".