Just as it says

Im in the BC interior and the 16k frequency works best. Instead of slapping at Mosquitos every 10 seconds its now only every few minutes. Very few Mosquitos come near me now with this going. Love it! I can hear the 14k & 16k frequencies though. Overall a good app that does what it says it does!

Tdoll23 about Anti Mosquito - Sonic Repeller, v1.5.1