Actually both. When you produce electronics, each device must pass an electromagnetic compatibility (EMC) test before you are allowed to legally sell it. It t

Actually both. When you produce electronics, each device must pass an electromagnetic compatibility (EMC) test before you are allowed to legally sell it. It test both the electromagnetic emission and the electromagnetic immunity of the device. So not only shouldn't the device emit more than a certain level of EM power, but it must also be able to withstand a certain field strength without losing functionality.