Short-Period Borehole Seismometer, Model 20171
This is a borehole version of the S-13 seismometer, having a generator constant of 650 V/(m/sec). It can be installed in boreholes up to 300 m deep, in any given inner diameter between 102.6 and 200 mm.
 

Short-Period Ultra Low Noise Borehole Seismometer, Model GS-21
This is a borehole version of the Model GS-13 seismometer, having a generator constant of 458 V/(m/sec). It can be installed in boreholes up to 300 m deep, in any given inner diameter between 102.6 and 200 mm. A newer version, Model GS-21A, with 2000 V/(m/sec) output, is now available.