SENSORS IDA uses a suite of sensors to capture the full range of geophysical information in the environment surrounding an IRIS GSN site. The sensors may be grouped into several broad categories: the principal broadband seismometer. At each IRIS/IDA station, either the STS-1 very broadband seismometer manufactured by G. Streckeisen AG or a triaxial KS54000-IRIS manufactured by Geotech Instruments, LLC is employed to record accurately very long period to mid-range seismic data. the auxiliary seismometer. Because the STS-1 and KS54000-I sensors do not record the higher frequency portion of the seismic spectrum with the sensitivity desired by the IRIS community, an auxiliary sensor is installed at many sites. The auxiliary sensor is either an STS-2, also made by G. Streckeisen AG, a CMG-3T by Guralp Systems Ltd, or a GS-13 also by Geotech Instruments, LLC. the strong motion accelerometer. The above seismometers will behave in a non-linear fashion when subjected to high accelerations. In order to record acceleration up to 2g with fidelity, a strong motion instrument is installed at most sites. The instrument in use at IRIS/IDA stations is the FBA-23 made by Kinemetrics Inc. other instruments. Because of the effect of air pressure on long period seismic recordings and because geophysical phenomena such as volcanic eruptions generate pressure waves of interest, it was decided to install microbarographs at GSN stations. The model used at IRIS/IDA stations is the 6016-B made by Paroscientific, Inc.