This application generates high frequency sound in the range (20000 Hz-22000 Hz) that is inaudible to most of the humans. However, insects like mosquito can here this sound and it is annoying for them so they do not come close to this device .

This is 3 in 1 application which can work as your: Night Clock, Alarm, Mosquito repellent.

http://appshopper.com/entertainment/good4night