Friendly Fire

Today's article about the danger to undercover police officers reinded me of my wartime work designing IFF equipment - Identification, Friend or Foe. We used coded electronic challengers and automatic responders so a fighter could quickly decide whether he had a target in sight. Those devices were bulky and expensive then, but cheap interrogators could easily be mass produced now. Responders would have to have frequently changed codes to prevent self-protection by miscreants. The policemen most in danger could be appropriately equipped. I conceive a system that would instantaneously issue an electronic challenge whenever a policeman's hand touched his gun. A response within milliseconds should abort even the quickest draw.