Evidence of failure of the error-proof device

Error-proofing devices have a simple objective to make products or process without any defects. If there is a defect of any kind, then the error-proofing devices are not achieving its objective. Then it is a failure.

You can make evidence on the paper report of device performance or using software to have it recorded. Most error-proofing devices have their software that is generating reports about performance. Those reports are fine evidence.

For more about error-proofing please read the article: 

How to establish an error-proofing process according to IATF 16949 https://advisera.com/16949academy/blog/2017/10/11/how-to-establish-an-error-proofing-process-according-to-iatf-16949/