Praise be to Allah.
Muslim narrated in his Saheeh (2113) from Abu Hurayrah (may Allaah be pleased with him) that the Messenger of Allaah (peace and blessings of Allaah be upon him) said: “The angels do not accompany any group with whom there is a dog or a bell.”
And he narrated (2114) also from Abu Hurayrah that the Messenger of Allaah (peace and blessings of Allaah be upon him) said: “Bells are the musical instruments of the Shaytaan.”
Al-Nawawi (may Allaah have mercy on him) said: As for bells, it was said that the reason why the angels dislike them is that they are similar to church bells, or because they are one of the hanging things that are forbidden. And it was said that the reason why they are disliked is their sound, which is supported by the report which mentions “the musical instruments of the shaytaan.”
The reason why their sound is disliked is that it is akin to musical instruments, which are forbidden.
Al-Haafiz Ibn Hajar (may Allaah have mercy on him) said: To sum up, the sound has two qualities, one which is the strength of the sound and the other is its tune, and because of its musical tune it was prohibited, and the reason was given as being because they are “the musical instruments of the shaytaan.”
Shaykh Ibn ‘Uthaymeen (may Allaah have mercy on him) said: (The Prophet (peace and blessings of Allaah be upon him)) told us that the angels do not accompany people with whom there is a bell, because when the animals walk, it will make a sound like music, and it is known that musical instruments are haraam. End quote. Sharh Riyaadh al-Saaliheen (4/340).
With regard to alarm clocks and the like, if they have musical sounds then they are haraam, because of the general meaning of the evidence that indicates that musical instruments are haraam. But there is nothing wrong with an ordinary alarm clock.
Shaykh Ibn ‘Uthaymeen (may Allaah have mercy on him) said: As for alarm clocks and the like that do not come under the prohibition, and things that are used beside doors to ask permission to enter – because some doors have a bell to ask permission to enter – there is also nothing wrong with these, and they do not come under this prohibition, because they are not hung around an animal’s neck and the like, and they do not create a tune which is the reason why the Prophet (peace and blessings of Allaah be upon him) forbade them. End quote.
Sharh Riyadh al-Saaliheen (4/340-341).
The Standing Committee was asked: What is the kind of bell that is forbidden? Please note that there are electric bells that make sounds like birds, or bells on alarm clocks where one piece of metal strikes another, and other kinds.
The bells that are used in houses, schools and so on are permissible, so long as they do not include anything haraam, such as resembling the church bells of the Christians, or have musical sounds. In that case they are haraam for that reason. End quote.
Fataawa al-Lajnah al-Daa’imah (26/284).
And Allaah knows best.