They’ll probably annoy your dog more than any insects. The manufacturers claim that the ultrasonic frequencies piped through the devices’ speakers are a chemical-free way to keep pests out of your house. There’s just one little problem: bugs can’t hear the noise. “It’s like trying to keep a kid away from sweets by playing Mozart,” says Dr Ulrich Bernier, a scientist with the US Department of Agriculture’s mosquito and fly research unit.
A smarter strategy, Bernier says, is to stop insects from invading your house in the first place. Put all your outside lights on motion sensors; that way you’ll reduce the number of flying bugs that hover around the lights at night and slip inside the house through open doors or windows. Make sure there’s no stagnant water collected around your garden, in empty pots or watering cans.
Inspect your foundation for cracks and broken seals, especially around exterior taps, pipes and electrical outlets. Patch any holes with an expanding-foam sealant.