Mr. Bear and KawAbuser are right. You have no chance with a deer. They are so fast they will blind side you.
They go from being absolutely still and camoflaged against the bush to an instant 40 mph across your path.
All you can do is ride slower to reduce impact force as you pass likely deer terrain (bushes, thickets, woods) during rutting time in the Spring, during insect infestations because that drives deer out of the woods, and in the Autumn when they are actively foraging to fatten up for the winter. If you are downwind in a strong wind, ride even slower because the deer can't hear you coming and they may bolt upon visual contact.
AS FOR THOSE ULTRASONIC DEER/MOOSE WHISTLES that mount on your fender, no one up here in deer & moose land (rural Ontario, Canada) uses them because they figure the noise excites and scares deer into action and makes a crash more likely.
IMHO, the best thing you can do is have noisy exhaust and very bright headlights...deer understand that language and know not to cross the road when a vehicle is coming.
It's the silent runners that surprise them and get nailed.