Elitzur–Vaidman bomb tester

The Elitzur–Vaidman bomb tester is a device that can help you tell if a bomb is real or not. It works by sending a beam of light into the bomb. If the bomb is real, then some of the light will bounce back—like an echo—and the Elitzur–Vaidman bomb tester will detect it. If the bomb is not real, then no light will bounce back and the Elitzur–Vaidman bomb tester will tell you it's not a real bomb.