I’ve got something like this as a home-plug which is designed for a range of 25 square meters and works on 230 volts so my guess is that the range for the USB version is just enough for keeping them away when you’re behind your computer. The home-plug version works quite well actually but is a bit noisy. Keep in mind that the devices are only effective against female mosquito’s because it’s said that they are the only ones that sting. So if any mosquito’s do seem unaffected the chance is that it’s a male mosquito and you have nothing to worry about except for the annoying sound thay make