On early pre-production Atari vector games, you could burn a hole in the phosphor all the way to the glass if you left the electron gun active too long without

On early pre-production Atari vector games, you could burn a hole in the phosphor all the way to the glass if you left the electron gun active too long without moving the beam. They added a "spot killer" circuit that turned the beam off if you left in place too long. (From "The Secret Life of XY Monitors": http://www.jmargolin.com/xy/xymon.htm http://www.jmargolin.com/xy/xymon.htm)