Radiation detection instruments comprised of 1) one or more gamma-ray detectors, 2) associated multichannel analyzers that collect and transmit the gamma-ray energy spectra, 3) a very small natural or man-made radioactive source to calibrate the gamma-ray detectors and ensure their proper operation, 4) an optional neutron detector, 5) an embedded computer to analyze the spectra and issue various alarm messages that include, among other information, the radioactive isotopes causing the alarm, 6) a network radio that provides for wired and wireless communications to transmit the alarm message to a local command center, and 7) commercial off-the-shelf rechargeable lithium-ion batteries. These components in their entirety allow tiny sources to be detected, identified so as to discriminate between naturally radioactive materials, persons who received medical treatments with radioactive materials and threats to public safety, and thus report potential threats in homeland security situations