Ultrasonic pest repeller side effects on humans  emit high-frequency sound waves to deter pests, and while they are generally considered safe for humans, there are some potential side effects. Prolonged exposure to high-intensity ultrasonic waves may cause discomfort such as headaches or nausea. However, most devices on the market adhere to safety standards to minimize these effects. It's advisable to follow product guidelines and consult with a healthcare professional if any concerns arise.