Methods, apparatus, systems and tangible computer readable storage media are disclosed to determine an operational status of a device. Disclosed example apparatus include memory and processor circuitry to execute computer readable instructions to at least measure with a first sensor, a first magnetic field in at least three dimensions, the first magnetic field including a device magnetic field caused by a wire attached to a device to supply electricity to the device, the first sensor proximately arranged to the wire, measure with a second sensor, a second magnetic field associated with an environment at least a first distance from the wire, and compare (a) the first magnetic field as measured by the first sensor arranged proximate to the wire and (b) the second magnetic field as measured by the second sensor.