Two can play this game
Tian Han nodded and looked happy as any other teenager proud of his work. "It can detect listening devices as well as hidden cameras."
Nana asked, "How does it work?"
Tian Han thought for a second and said, "Well, there are many apps that can detect such devices. But the problem is that you have to sweep your phone in all directions so that your app catches the signal of the hidden recorder. It will alert you for sure, but if there is a hidden camera, then obviously the perpetrator can see you. Your sweeping action will let him know that you are suspicious of the presence of any camera."
Nana nodded.
"It isn't a problem with purely listening devices. They can't see you. So you can quietly check for any devices. I have created a spy device detector and tweaked it a bit. My girlfriend won't have to remove her phone and sweep the area. She can keep it in her purse, and if there is a spy camera, then it will vibrate, telling her of its presence."