Methods and apparatus to determine an operational status of a device

A tangible computer readable storage medium comprising instructions that, when executed, cause a processor to at least:

• measure a first magnetic field associated with a wire at a first distance from the wire, the wire to supply power to a device;
• measure a second magnetic field at a second distance, greater than the first distance, from the wire, the second distance to reduce detectability of the first magnetic field by the second sensor;
• compare the first magnetic field measured at the first distance and the second magnetic field measured at the second distance to determine an operational status of the device;
• and
• collect audience measurement data based at least in part on the operational status of the device.

An apparatus comprising:

• first measurement means to measure a first magnetic field associated with a wire at a first distance from the wire, the wire to supply power to a device;
• second measurement means to measure a second magnetic field at a second distance, greater than the first distance, from the wire, the second distance to reduce detectability of the first magnetic field by the second measurement means;
• comparing means to compare the first magnetic field and the second magnetic field to determine an operational status of the device;
• and
• collection means to collect audience measurement data based at least in part on the operational status of the device.