The front door of the flat where we lived in Mumbai was fitted with a peeping hole. The person inside upon hearing the bell could check through this glass hole to ascertain who is outside. It was for security purposes. We never knew that this device is called Judas, or Judas hole or Judas peeping hole.
Must be remembering the Judas Iscariot, one of the twelve disciples of Jesus. It was he who is said to have betrayed the Lord. The device is named after him. Judas or Judas peep hole or Judas spy aperture is a device which is fitted in the door. Although these holes allow both the outsider and insider to peep through, Judas hole is considered one way. The person from outside can Spy on the inside.
The device gets its name from Judas Iscariot the twelfth disciple of Jesus. Judas betrayed Jesus on Wednesday when he in lieu of some money told the whereabouts of Jesus and agreed to hand Jesus to Sanhedrin. Spy Wednesday gets its name because this is the day on which Judas betrayed Jesus to the Sanhedrin. Because Judas is thought to be sneaky, his actions conjured up the image of a spy.