Doorbells are useful for the convenience and safety they provide, alerting you to the presence of a guest while still allowing you to keep your doors securely locked. While doorbells are simple in their construction and operation, they can still fail from time to time. A doorbell that buzzes without producing its normal ringing sound may be having an electrical or mechanical failure.
Some broken doorbells will fail to produce any sound at all. However, in other cases a doorbell will make a faint buzzing sound, either at the location of the bell inside the house or, in a wireless doorbell system, through a speaker attached to the outside doorbell button. The buzzing, which you may need to be close to the doorbell to hear, indicates there is still a connection between the button outside and the bell itself. However, the fact that the sound doesn't occur at its normal volume makes the doorbell only partly functional.
Lack of Power
One of the possible reasons for a doorbell to buzz without ringing is a lack of sufficient electrical power. Doorbells require a minimum voltage, which is usually significantly below what your home's electrical system provides, to operate. If you have a battery-powered doorbell, changing the batteries may address the problem. In other cases, your doorbell may have a bad connection or frayed wires between the button, your home's electrical system and the ringer inside.
Another reason for a doorbell to buzz without ringing normally is some type of mechanical issue. This won't occur with fully electronic doorbells that create sound using speakers. Instead it applies to those that have a physical bell, with a reciprocating hammer that strikes a stationary bell to create the ring. The hammer may be blocked due to rust or debris. It may also break, preventing it from reaching the bell.
Some homes have wireless doorbells that communicate using radio signals. These types of doorbells are useful when the front door is far from the bell inside the home, as with a bell on a driveway or sidewalk gate. Wireless doorbells may produce a buzzing sound as feedback for the visitor while simultaneously causing the bell inside the home to ring. If the two devices can still communicate, but the bell inside has a mechanical or electrical problem, the visitor will hear a buzz without the bell inside ringing.