answer:I have installed various apps like that, both on computer and on mobile phone. And I have noticed one thing in common: they all only work for some days, after that mosquitoes come back, maybe fewer in number, but they still come back. It makes me suspect the effect of the apps. Maybe the mosquitoes just get used of the sound. And yeah, sometimes you can hear the sound. One app I used had a tendency to make sound I could hear one day then no sound another day, although I always chose the same frequency. I’m wondering how it was possible. The sound was a high pitch sound that was very unpleasant to the ears. I didn’t get headache but it was very annoying. I don’t know any scientific proof behind these apps, but from my personal experience, they aren’t worth it. You can use smoke and it works better. And BTW, my dad claimed that one app seemed to disrupt the function of his other apps in the phone, so he deleted it.