A good way to detect hidden cameras and microphones is to use a smartphone with a built-in magnetometer sensor. The app will detect any magnetic field changes and let you know with a beep.  The best part is that you can use the app to scan your whole room. This will help to detect the magnetic field changes caused by the devices. The free Anti Spy Cam can also be used as a locator and device finder for electronic devices such as smartphones, laptops, and televisions. 

The app can also locate hidden cameras and microphones in your home or office.