Rodent and bug repellers are mostly plug-in devices or corded units. The corded units are generally quite expensive, but they are known to more effective. The ultrasonic repellers emit sounds with a high frequency of 20,000 Hertz which disturb pests who have sensitive hearing.

Apart from the ultrasonic repeller, you will also find the electromagnetic repeller in the market. This emits electromagnetic radiation which affects the nervous system of common insect pests and rodents. 

After going through several reviews of ultrasound rodent repellers, we have found out that most users look for these four things while buying the products.

• Customer service: Always select a company which has good customer service. Post-purchase service matters a lot for these devices, and a product with a good warranty can be easily replaced in the event of malfunctioning.

• Easy installation: Choose a product which is easy to install and meets your requirements. A one-size-suits-all-purpose pest control device is probably one of the easiest methods of pest management at present.

• Energy consumption: Buy a product which consumes less electricity. Along with good quality and a good design, you also need to find out about its electricity consumption. Otherwise, you might end up paying an exorbitant electric bill every month.

• Look for a free trial: A number of factors can influence the effectiveness of any device: temperature, position, other sounds in your home environment, and even the layout of your home. You cannot be certain if the product will work in your home environment unless you try it yourself. If the company offers free trials of their products, do not hesitate to use it before installing one.

• Do your own research: According to the Federal Trade Commission, the manufacturers of ultrasonic rodent repellers must back their claims with scientific evidence. You need to dig deeper before you finalize on a product. Choose a pest control device which has good positive reviews from verified buyers. It is better not to be persuaded by bombastic claims. Rather, look for proof which establishes the fact that the company has conducted individual experiments which validate the claims of the repeller.

• The area that needs to be covered: If you are planning to clean a cluttered apartment or a densely-populated place, one device will not suffice. Keep in mind the total action radius--a smaller device may be adequate for removing spiders, but for the band of squirrels in the attic, you will need probably more than one ultrasonic repeller.

• Think about the expenses: Think about your budget before buying the product: take the middle path and choose something which will neither be too inexpensive nor too costly. A cheap rodent repeller does not sound promising, but spending too much on the device can be risky as well since you are unsure about the results.

• Choose your location: The repellers emit both strong and weak sound waves which can be easily obstructed by furniture, walls, or corners. In order to fully remove the pests and rodents, you might have to use the device along with traditional traps.

GreenGuard: Known as one of the most popular brands, offering all kinds of pest control solutions, the GreenGuard ultrasonic rodent repellers are environment-friendly and noiseless. These devices offer non-toxic solutions to control pests without affecting the health of your pets or children. They use the most sophisticated technology—that is, electromagnetic and ultrasound waves--which are even effective from behind a blocked wall or ceiling.

T3R: The T3R Triple High Impact Repeller is sold by TMC Pest Repeller, and is known for its unique design with three speakers. Customers have vouched for its excellent post-purchase service. A 6-foot extension cord makes it easier to place the device in various places.