The device shown here is a two-pole tester from www.picoauto.com
It could be the piece of equipment that does the most important test you will ever carry out! The test that stops you being killed by electric shock. The device is deliberately very simple. The image top left is a test with the leads connected together. The next image is a safe 12V reading but the bottom image shows a dangerous reading (mains voltage with my PV panels working in this case).
Simple go, no-go results.