no bells to signal prayers and such, in islam,. muslims are called through prayer by a vocal call
musical instruments can never be as beautiful and eloquent as the human voice:

what the muezzin(the person calling the adhaan)
(many desiz call it aZaan (the arabic huroof (letter) is not zaal, it is dhal))
is saying and its translation:

Recital Arabic Transliteration Translation

4x الله أكبر Allahu Akbar Allah is the greatest*

2x أشهد أن لا اله إلا الله Ash-had anna lah ilaha illallah I bear witness that there is no deity except Allah

2x أشهد أن محمدا رسول الله Ash-hadu anna Muħammadar rasulullah I bear witness that Muhammad is the Messenger of Allah

2x حي على الصلاة Hayya 'ala-salah Make haste towards worship

2x حي على الفلاح Hayya 'ala 'l-falah Come to the true success

(2x*الصلاة خير من النوم Al-salatu khayru min an-nawm Prayer is better than sleep *)fajr prayer only

2x الله أكبر Allāhu akbar Allah is the greatest

1x لا إله إلا الله La ilaha illallah There is no deity except Allah

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The adhān is the Islamic call to prayer, recited by the muezzin. The root of the word is ʼḏn "to permit", and another derivative of this word is uḏun, meaning "ear."

Adhan is called out by the muezzin in the mosque, sometimes from a minaret, five times a day summoning Muslims for mandatory (fard) prayers (salah). There is a second call known as iqama (set up) that summons Muslims to line up for the beginning of the prayers. The main purpose behind the loud pronouncement of adhan five times a day in every mosque is to make available to everyone an easily intelligible summary of Islamic belief. It is intended to bring to the mind of every believer and non-believer the substance of Islamic beliefs, or its spiritual ideology. Loudspeakers are sometimes installed on minarets for the purpose.

The adhan sums up the teachings of Islam. In the Qur'an and the sunnah there are four fundamentals on which the entire superstructure of Islam rests:
(a) Belief in the oneness of Allah and in the fact that there is no Power greater than Him;
(b) he alone is the Creator and the Master of the universe and no one other can claim share in His Godhood of sovereignty;
(c) Muhammad is the final dispenser of the Will of Allah and it is his words and deeds that His will find expression;
(c) it is not the material utility that determines the value of things or acts in Islam but their spiritual significance - thus salvation in Islam lies in the purification of the soul which can be achieved only by willing and conscious obedience to the Commands of Allah, and prayer is the most important of that obedience; (d) the highest aim of the life of a Muslim is to live a life of a eternal bliss. (less info)