Ask Mr. Smarty Plants

There is a lot of material out on the web if you search for something like "sound devices to repel deer." The general agreement is that both motion devices and sound devices work - for a while. Deer are smart enough to figure out fairly quickly that the devices pose no real danger and then they ignore the commotion.

Here is an excerpt from a publication of the Delaware Departmnet of Natural Resource that summarizes both motion and auditory devices:

Auditory Deterrents 

Auditory deterrents can repel deer with their noise, and include noisemakers like gas or propane exploders, whistles, and ultrasonic devices. Gas or propane exploders produce loud, banging noises, which frighten deer away, and have been used to help protect orchards, row crops and truck crops. The most effective exploders detonate at random intervals and /or rotate the direction of their blast to prevent deer from getting used to them. Most auditory deterrents should not be used in suburban or residential areas out of consideration for neighbors - their use should be restricted to rural areas where noise is not a problem. 

A radio, activated by a motion detector can also scare off deer. Pie pans or metal cans suspended by strings make noise when they rattle in the wind, and have also been used to deter damage for short periods of time. Motion activated ultrasonic noisemakers scare deer using high-frequency sounds which are inaudible to humans, and don’t violate noise ordinances. Field trials of some of these products showed that they were effective at deterring deer damage initially, but over time, deer became habituated to the sounds they emitted and were not repelled. 

Auditory deterrents may be useful in temporarily scaring deer, but may need to be combined with visual deterrents and / or repellents to be effective at deterring persistent deer. 

Visual Deterrents 

Visual deterrents include scarecrows, flashing or strobe lights, helium-filled Mylar and “Scare-eye” balloons, Mylar tape and flagging that moves with the wind, and motion activated water sprayers. Mylar is a shiny plastic material that reflects light and makes noise when the wind blows across it. 

Scarecrows work on the principle that deer fear humans, but may lose their effectiveness where deer are accustomed to seeing people. Odor-based repellents or motion can be added to scarecrows to increase their effectiveness. Visual deterrents that move may be more effective at deterring deer, as deer readily detect and react to movement. Helium-filled “Scare-eye” or Mylar balloons, flagging and Mylar tape have also been used to deter deer damage. It can be hung from stakes or plants like streamers to scare deer. Mylar tape twisted into a spiral, and suspended between posts, makes a buzzing sound when the wind blows over it, which can help deter deer. 

Infrared motion sensors and / or timers can be used to trigger scare devices, which can scare away deer. Flashing and strobe lights, and water sprayers or sprinklers activated by motion sensors, or set on timers, can also deter deer. The Smart Crow MotionActivated Sprinkler, Contac Scarecrow Motion Detector Sprinkler and Spray Away Motion Activated Water Repellent are some commercially available sprinklers designed specifically to ward off deer and other nuisance animals. 

Remember that auditory deterrents combined with visual deterrents and / or repellents may be more effective than any one type of deterrent used alone.

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Mr. Smarty Plants is thinking of applying for a patent for a device that makes a sound like a mountain lion's tummy growling.