I had the manual deer whistles mounted on my Gold Wing for awhile, but I'm not sure how effective they are, and apparently you have to be moving at a minimum of 35 mph before they start to "whistle" anyway. Then I got one of the electronic "Deer Alerts" and installed it on the Wing. Now that can be heard, at least by people. The theory is that deer can hear them as well, from a claimed distance of up to 400 yards. The other part of the theory is that even though it just emits a tone, it's supposed to be at a frequency that the deer don't like, so they either don't move or they avoid it by running off. Like I said, theory. To my knowledge, no one has interviewed a deer to find out if it's true.
Personally, there is no substitute for keeping a sharp eye out for the critters, especially deer, because they are stupid and so unpredictable. One should not rely solely on a set of deer whistles, either the manual ones or the electronic ones. I think, in the end, that it boils down to, if you think they work, then they work. I do know that they are extremely effective on elephants, because all the time I had the whistles and the electronic unit, I never saw an elephant alongside the road.
"Don't sweat the small stuff---it's all small stuff"
'09 650 VStrom