We tested bh HPM hybrid detectors and bh PMCS PMT detectors for IRF changes induced by external magnetic fields. The effects were found surprisingly small. For a magnetic-field strength on the order of 100 Gauss the shift in the IRFs was between 1.75 ps and 14.5 ps compared to the field-free case, depending on the direction of the field. The FWHM changed from 16.4 ps to 18.4 ps for the HPM and 97 ps to 109 ps for the PMCS.