1. When the switch closes, current flows through the coils, magnetizing the inner iron core.
  2. The iron armature on the sprung striker arm is attracted by the electromagnet; the bell sounds.
  3. The contact points separate; current flow in the coils ceases; the electromagnet turns off.
  4. The spring returns the armature; the contact points close; the coils renervate.
  5. The cycle repeats and the bell continues to ring while the switch is held down.