Ultrasonic mosquito devices repel mosquitoes by emitting a high-pitched noise similar to a dragonfly, the mosquito's natural predator. One form of ultrasonic mosquito deterrent is called the Sunbeam CM160 Electronic Mosquito Repeller which claims to repel mosquitoes from of a distance of up to 75 square feet. Virtually all forms of ultrasonic devices are portable due to their small size and are commonly sold as wristbands, belt clip-ons, table-tops or key chains. Both electric and battery operated mosquito repellers can be purchased for between $5 and $15 online. Before purchasing this form of mosquito repellent, it's important to note that many consumers have found this method of mosquito repellent totally ineffective.