Both reports from the National Institute of Standards and Technology (NIST) are available online and describe authentication mechanisms that protect your sensitive data.
"Proximity Beacons and Mobile Device Authentication" (NISTIR 7200) describes how two different kinds of location-based authentication mechanisms that use signals from wireless beacons can be used to authenticate handheld device users. If the user is in an unauthorized location or a location outside a defined boundary, access will be denied or an additional authentication mechanism must be satisfied before gaining access.
While many organizations use smart cards for security, they require a card reader that can be nearly as large as the handheld device. "Smart Cards and Mobile Device Authentication" (NISTIR 7206) describes two types of smart cards that use standard interfaces supported by handheld devices, avoiding the use of more cumbersome, standard-size smart card readers.
Both reports are available at http://csrc.nist.gov/publications/nistir/index.html.