What is the smiley face sensor at the stern of the F-4 Phantom? The F-4 Phantom has an interesting collection of sensors at the extreme rear of the empennage. What are these sensors for? My daughter calls them them smiley sensors but I suspect that is not the proper technical term. Her guesses as to their real purpose:


Detect other airplanes.
Detect smiles.


Which one is it?
Your daughter is right as explained here:


  The 'bug-eyed' face of the parabrake door mounting the two
  rear-hemisphere radar warning antennas.


So they do detect other airplanes and probably the smiles of their pilots too as they are getting close to the phantom.