I was recently at a Poker Run and was told a story about a guy that was able to slow down to avoid an initial impact with a rather large buck during rutting season. However, the buck started running along with him and tried to attack him. He was able to accelerate away but not before he and the bike got some blood and hair on them.
Myself, I've hit a couple of deer in my truck but never on the bike. Did not have whistles at the time, and still don't. The consensus up here is that the whistles don't work. I think the best defense is just to be hyper aware. I've driven around probably a hundred deer and only hit two. Those two just bounded out of nowhere.

 

It will make them pick up their heads and take notice but around here at certain times of the year the bucks have one thing on their mind and nothing you can do will get them to change their minds.

 

I live in Deer Country. A few years back I got some vance and hines slip-on, saw some deer on the road, tweeked the throttle and spooked the stink outta the deer. But like another poster said they're likely to run in any direction.
"Loud Pipes Spook Deer!"

 

They do not work on my deer magnet Suburban. Deer are like rats with long legs. If you miss one then the second or third will get you. I don't ride at night...

 

i put some on my truck and hit 4 deer that year within 6 months,never used them again they dont work IMO.......

 

Thanks for all the great posts and the article...I recall reading the article but assumed they were mostly speaking of the chap wind driven ones and not the newer technology. It seems the more people you ask the more differing opinion you get. Met a guy 2 years ago who had the hornet system...told me he noticed that when he had his on he would notice that it would disturb the grazing deer and they would scatter...many times right at him....seems other have the same opinion. I installed mine 3 years ago and honestly don't run it all the time...never had a deer bound out in front of me while running it.... bought it cause I did have a deer bound out in front of me.....does it work...I don't honestly know....but I will say that no matter wheat I attach to the front of my bike to keep deer away I am still going to continue to be extra careful in night time situations especially along rural or heavily wooded areas close to the road....So anyone know a a good system to keep bears from bounding in front of you...LOL

 

The company that makes the top-rated deer whistles also makes a great aerosol elephant repellent. It really works....I've been spraying it in my back yard and haven't seen an elephant yet.

 

Now I know why I've been get'n so many elephants in my yard!!!!

 

Bottom line is if anything worked, the insurance companies would give them to you free! You have any idea how much deer damage cost the insurance companies? (you really)

 

http://www.ibmwr.org/otech/deerw.html