More and more devices are using USB as a power supply despite the fact that they are completely unrelated to computer use. One such recent addition is the USB mosquito repellent dongle
. Similar to other electronic pest deterrents, this device generates a repellent field to which some insects
Plugging this into any powered USB port should repel most flying insects according to manufacturer. This technology has not, however, received much commercial success. Even if it has only a limited effect, the repellent USB dongle is an incredibly cheap function to implement. That being said, it's very hard to imagine many situations where having a mosquito repellent while doing computer related work would be of much help. But again, for the six dollars that one of these costs, you could very easily keep one around just in case you found any such coincidence.