Ultrasonic spikes emit loud, high-pitched sounds that voles don't like. While brands vary, the sound is typically an ultrasonic frequency of about 400Hz. These frequencies cannot be heard by humans and other animals such as birds and dogs, so the product can be used without worrying about bothering anyone or having any effects on pets or plants – only voles will take notice.
Some of the best sonic repellent devices can cover a radius of up to 40-50 feet - and many people find they work better than other pest programs because they don't rely on chemicals that might affect pets or plants!
Pros
Loud noises repel pests naturally.
No need to use harmful chemicals.
Cons
Can be pricey for some people on a budget. Can also affect pets or plants with sensitive hearing if placed too close by accident - so make sure you know where they are before turning the device on!