The GLAST Burst Monitor includes 12 Sodium Iodide (NaI) scintillation detectors and 2 Bismuth Germanate (BGO) scintillation detectors. The NaI detectors cover the lower part of the energy range, from a few keV to about 1 MeV and provide burst triggers and locations. The BGO detectors cover the energy range of ~150 keV to ~30 MeV, providing a good overlap with the NaI at the lower end, and with the LAT at the high end. Together the NaI and BGO detectors have similar characteristics to the combination of the BATSE large area and spectroscopy detectors but cover a wider energy range and have a smaller collection area.

The detectors will not block any part of the Large Area Telescope (LAT) field-of-view (FOV) nor interfere with the solar panels. They easily fit between the LAT and the shroud envelope on two sides of the spacecraft. The mounting arrangement is flexible with the two BGO detectors mounted on opposite sides of the spacecraft, and the NaI detectors mounted in 4 banks of 3 detectors in such a way that they sample a wide range of azimuth and elevation angles.