A device includes a field-detecting component, an input component, an accessing component, a comparing component and an identifying component. The field-detecting component can detect a field and generate a detected field signature based thereon. The input component can input the detected field signature into a database. The accessing component can access the detected field signature from the database. The comparing component can generate a comparison signal. The identifying component can identify item or location based on the comparison signal. The field-detecting component can further detect a second field and generate a second detected field signature based on the detected second field. The comparing component can generate the comparison signal based on a comparison of the detected field signature and the second detected field signature.