Q. I’m thinking about ordering this device I saw advertised that says it repels cockroaches with sound waves. Do these things work? If it doesn’t work, how can they sell it?

A. The devices you’re talking about are sold by various names: ultrasonic devices, electronic pest control systems, electromagnetic pest repellers, and others. The device is usually a little black plastic box that is plugged into an electrical outlet. A red blinking light supposedly lets you know that it’s working. Their manufacturers claim that they will repel a wide range of pests using only irritating high frequency sound waves, or vibrations, or electromagnetic output. The companies also claim that the devices will not affect humans or pets. That’s true but they don’t affect insects either. Most insects do not have “ears” and have no way to detect ultrasonic sound.

The scientific evidence says the devices don’t work. Every university research project that has looked at any of these devices found that they were ineffective. Studies found that not only do the devices not repel cockroaches; they don’t even affect cockroach behavior or their distribution within a room. One of the best comments about the effectiveness of an electrical pest control device came from the state of Texas, which stated in court “The device is a hoax and stands on the same scientific footing as a perpetual motion machine.”

The Environmental Protection Agency that regulates pesticides does not regulate pest control devices, so manufacturers don’t have to submit efficacy data. Some of the product manufacturers have been prosecuted by EPA or the Federal Trade Commission for making false claims. But there are simply too many of these devices for the government to challenge or prosecute them all. The FTC sent letters to more than 60 manufacturers of ultrasonic pest control devices, stating that their efficacy claims about these products must be supported by scientific evidence. FTC specifically challenged the advertising claim, “repels insects.”

Then why do there seem to be so many satisfied users in the ads? Some of it is wishful (or hopeful) thinking. And some of it is that insects come and go. They are famous for appearing and then disappearing. Ants are especially fickle. Many things affect insects’ reproduction and life cycles. When they disappear, credit is given to whatever pest control method was in use at the time. Usually the credit is deserved but sometimes the insects would have died out or left anyway, regardless of what was thrown at them.

The bottom line is that these electronic devices do not work against insects, including cockroaches, ants, and fleas. If you have a pest problem, spend your money with a respected professional pest control company instead. They come with a guarantee.