To be certain they are functioning properly, NSA Guidelines suggest that degaussers “should be re-tested periodically according to manufacturer’s recommendations”.
Many new degaussers feature a magnetic field strength indicator that provides instant feedback to the operator. If the indicator displays the minimum required field strength or greater, the unit will display a PASS/FAIL based on the field strength. Users can then be certain that the degausser functioned properly. Because of this, many manufacturers no longer recommend retesting/recertification. However, for an added measure of security, some users do choose to periodically retest.
Different manufacturers retest in different ways. Some use a low density VHS or Data Tape. However, the most thorough and accurate recertification is completed using a High Density Hard Drive. The process is fairly simple a drive is degaussed in the customer’s unit and then sent to a forensic laboratory where experts search for remnant data using sophisticated test equipment. If no evidence of data is found on the drive, the degausser is recertified. If the forensic lab finds remnant data the findings are reported and the degausser should be taken out of service until it can be inspected and repaired by an authorized service technician. Upon completion of service the test process should be repeated.