Mosquitoes, do you hear?. Review on Ultra Sonic Mosquito Repellent

The door to door vendor thrust a sale on me, handed me this contraption and said Just plug it on and go to sleep. Said it emitted some high frequency sound repulsive to mosquitoes so they keep far far away. Will take me close close to sleep.I plugged in the gasket the size of a soap box. Except for a tiny red lamp there was not much to tell it has started its work. Others in the house had different observations. One said he could almost hear a whirring sound. Another said she saw a huge number of mosqs flying out of the house in a hurry. Yet another slapping himself said the number has dwindled. I was amused at these comments all the while watching a cloud of mosqs circling the new gadget investigating inquisitively.Hoping and convincing myself that it might take a while for the gadget to come to steam, I took asylum in the good old mosquito net. Long into the night I suspect I heard a whining sound around the gadget. Was it the mosquito music Or was it the repellent's own ultra sound?