The cellular Radiation Detector - Magnetic Field Detector is the best app if you want to detect Electromagnetic field in your surroundings.
Detects cell tower radiation and extremely low frequency electromagnetic fields.
it is also detect magnetic field in your areas. it is also alert when EMF field is high.
Magnetic Field Detector uses sensor magnetometer. it is detect electromagnetic field.
scalar product between two vectors to be zero either one of them is the zero vector or they are perpendicular to each other. Therefore the electric and magnetic fields are perpendicular.
Note:- Keep away from metal your mobile