I looked into deer avoidance products a couple years ago. At that time, and I'm not aware of any new information (tests, studies, etc) to the contrary, there is ZERO evidence that deer whistles of any kind work.
There is LOADS of ANECDOTAL testimony about how deer whistles mounted on vehicles have saved deer from extinction, but there is no science that supports anything more than correlations and speculation.
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Now, for some fun. >
If you do buy the deer whistles, let me know...I've got a new product in prototype you might be interested in:
Left Turner Whistles
Texter Whistles
Cell Phone User Whistles
Finger Nail Painter Whistles
The list is quite extensive. If you've got a hazard animal, we've got a solution! Each device costs only $1.99 and comes with a signed certificate of authenticity that it DEFINITELY MAY help to reduce collisions when used in conjunction with INCREASED DRIVING AWARENESS by a licensed driver of a fully maintained vehicle while traveling at or below the speed limit on sunny or VERY well lit roads that are bordered by 30 foot tall fences on both sides. Whistles are intended as a profit making device ONLY and make no claims to DEFINITELY do anything other than create profit for the seller. Seller will not be held liable for any or damages incurred with or without proper use of product. Seller will deposit all profits directly into private bank account and will ATTEMPT not to chuckle while so doing. .... ??? .... Lack of chuckling by seller cannot be guaranteed, but we'll try. No, really. We will TRY.