I've tried the electronic as well as the air whistling type and my conclusion is that during "rutt" (the mating season) and during the first week of hunting season, they just plain run amok irregardless of warnings & whistles.
The females run from the pursuing males and the males chase both the rivals and does. Hunters in the woods cause them to go on the move too. I only bring this up because I've whacked 2 and barely bumped 2 (in other vehicles) and all of these occurred during the mating season, with whistles and with electronic devices.
The 2 that I whacked jumped off of hill-sides much higher than the roadway where they were entirely out of view with no chance of seeing their gleaming eyes and thus no warning.
One that I bumped occurred when I saw a deer rush out up ahead of me and as I hit the brakes and downshifted a second deer came out and I barely bumped it with no damage to my fiero.
The second one I bumped occurred because of road conditions..freezing rain...I saw 3 deer about to cross the road and try as I might on black ice I couldn't avoid bumping the 3rd one bringing up the rear even though I crossed the centerline and went over to the shoulder of the opposite lane...still tagged it!
The best defense is to drive as much as you can with your high beams on and at reduced speed. So far its worked for my VX!