A tag includes a housing, an antenna disposed within the housing, and circuitry within the housing that is electrically coupled to the antenna. A battery within the housing is electrically coupled to the circuitry, the battery being positioned so as to avoid significant interference with electromagnetic fields associated with the antenna. A tag holder can be detachably coupled to a radio frequency tag, and has structure facilitating attachment of the tag holder to an object other than a tag. A tag includes a circuit and an antenna, the antenna having a plurality of conductive segments and capacitors that are coupled in series to form an endless loop.