They are useless, according to an article I caught in 'Ride Metric'? magazine I believe it was called...about 1.5 yrs ago (didn't suscribe to it, picked it up while on a trip..) The article was very informative, approached scientifically, using experts in audio, deer behavior- researchers, etc. They also noted *dozens* of universities & public safety agencies from around the nation that had done their own testing..they all reached the same conclusion...not even worth a buck, even if you had the doe...(sorry, couldn't help it!). Despite all that, my brother still turns on his electronic one when we go through the forest...guess its a 'feel good' thing..