• Doorbells contain solenoids, a type of electromagnet.doorbell image by fafoutis from Fotolia.com
  
  Doorbell electromagnetic hammers are constructed using a variation on the basic electromechanical solenoid design. In a solenoid, an electromagnet moves an iron-based metallic core rod to create physical movement. A solenoid also has a built-in counterspring that pushes the core rod back into place when the power stops flowing to the electromagnet, resetting the device to its resting position.
  
  

Solenoid Doorbell Hammers

• Solenoid bell hammers are just simple solenoids with an expanded-upon solenoid core rod and a hammer-striking face. These hammer-faced solenoids strike a bell inside the doorbell case and cause the doorbell to chime. The sound produced has just as much to do with the size and shape of the bell struck as it does the actual hammer itself. The most common type of striking head is a half-sphere head, much like the end of a ball peen hammer.
  
  

Single Action Doorbell Solenoid Configurations

• A single-action doorbell solenoid is the most basic configuration for an electromagnetic doorbell hammer. Most single-action solenoid hammers create a single tone by striking the bell, though it may do so in rapid succession to make for a more noticeable ringing. Single-action doorbell solenoid configurations are common among inexpensive, simplistic doorbells. It is possible to combine two inexpensive single-action solenoids and two bells in series to provide an inexpensive alternative to a double-action solenoid hammer while creating a similar effect.
  
  

Double-action and Pair Doorbell Hammer Configurations

• Double-action solenoids are solenoids engineered to move the central rod in two directions by changing the polarity of the electromagnet. A double-action solenoid has the capacity to strike two separate bells, making for a two-tone doorbell with the hallmark "ding-dong" sound. Double-action solenoids are common on mid-price and high-end doorbell products. High-end doorbells may even employ a few double-action solenoid hammers in sequence to create more elaborate tonal effects.