If you want to measure electromagnetic field around you, EMF Detector - EMF Meter and Magnetic Field Detector is the best choice. The app uses your phone's built in sensor to detect Electromagnetic waves around you. To use the EMF Detector, you just have to move around your phone in your room or in your surroundings to find out if there are any EMF radiations.
WonderTech Studio is the developer of this application which can be found in the Tools category. Over 100K users downloaded and set up the app and its latest release was on Nov 27, 2017. The average user rating of EMF Detector is 4.3.